an unprofitable Dick

Elizabeth has never insulted him to his face before the first proposal, though, so he's definitely not gonna think she'll do that in their marriage. That's why he's so shocked when she does insult him in her rejection—she has never done it before.

Unlike the rest of the Bennets save Jane, Elizabeth is polite and follows social etiquette. She only skates on the line of impertinence in a way that simply comes off as playful banter and teasing. She openly disagrees with Darcy sometimes, but that is not the same thing as insulting him, and never does it to him in an overtly rude way. Even when she tells him his flaw is to hate everyone, I don't think that has to be read as an insult, just flirting, because he smiles at her when she says it and immediately afterwards thinks he was too attentive to her. To him in these moments, they're either just having a discussion or flirting, and at worst she seems annoyed with him a couple times, no big deal.

Now, Elizabeth herself does insult her manners at the end, but she's doing it in a playful self-deprecating flirty way, and Darcy obviously doesn't agree with her read of herself, nor do I:

“My beauty you had early withstood, and as for my manners—my behaviour to you was at least always bordering on the uncivil, and I never spoke to you without rather wishing to give you pain than not. Now, be sincere; did you admire me for my impertinence?” “For the liveliness of your mind I did.” “You may as well call it impertinence at once. It was very little less...

The only characters that think that Elizabeth has bad manners are Miss Bingley, Mrs. Hurst, and Lady Catherine, and we certainly can't take their reads as being fair ones!

In fact, not only does Elizabeth not insult Darcy, but there are times when Elizabeth actually says seemingly nice things about him in front of his face, such as when she calls him "a man of sense and education," says he is "all politeness," or comes to his defense when Mrs. Bennet starts insulting him at Netherfield during Jane's illness. Elizabeth also says things to him which seem very flirty, like when she turns down his offer to dance a reel in the cutest way possible.

So, to go back to your original question, OP, about what Darcy thought his marriage with Elizabeth would be like, he probably thought they would continue to have spirited discussions in which she sometimes disagreed with him and sometimes teased him, which sounds fun, and overall she would be affectionate to him because he's seen she has a loving heart toward her family, and thus everything would be unicorns and rainbows 💕

Which makes it sooo delicious when she turns him down and he gets to find out he was utterly wrong 😈

I'm a realist, and so was Jane Austen; no one romantic will like this answer:

The couples, who are in love, lack birth control, and believe children are a gift from God, will have as many children as their fertility allows. The average in the era for a gentry family was 6.7 children. Anne Elliot, who may not always be able to travel with her husband, may have bigger gaps as a navy wife (I always have speculated that Mrs. Croft's one time away from her husband was because she was pregnant and maybe miscarried.)

As for names, Jane Austen adheres pretty closely to naming children after their parents, in almost every case where we know the parents' names and then using other very common names for the era. So it's going to be a whole crowd of Elizabeths, Annes, and Marys, Charleses, Johns, and Williams. The most exciting you'll get is a mother's maiden name being used as a boy's first name (like Fitzwilliam Darcy) and maybe Marianne Brandon using names from poetry.

Catherine Morland is the eldest daughter of ten (NA)

The Musgroves (P) and Lucases (P&P) seem to have very large families, but not all children are named. We know Charlotte Lucas has multiple brothers and sisters from the text, including Lucas Wine Boy. The Middletons in S&S I think have quite a few children already and they wouldn't be done.

The Bennet girls are so close I don't think it's possible to have deceased siblings between them. It's possible there were miscarriages or otherwise after Lydia. We do know of one stillborn, Sir Walter's son from Persuasion and we know of a single deceased sibling, Mary from Mansfield Park.

Secondary infertility would have been more common without medical intervention. We also know that couples who didn't marry for love did stick to that addage of "a heir and a spare" which may explain some of the smaller families.

Anne: like a 3/10. i think she has many offline pursuits that take up more of her time. she has facebook and instagram accounts but posts rarely. most of her screen time is used on the NYT puzzles, in which she has absolutely ridiculous streaks. also a recovered tumblrina

Wentworth: 7/10. again I think he has other pastimes, but he needs social media because he has a lot of friends that live super far away. he has really cool-looking IG stories but then sadposts about missing Anne on his close friends at 3 AM. also a regular twitter user

Sir Walter: 11/10. cannot live without tiktok. specifically i think he’s obsessed with those color analysis videos and judges people for not dressing for their color season. has a sizable amount of followers for being “that mean old guy with crazy drip"

Lady Russell: 6/10. she likes to keep up with people and she will occasionally get caught up scrolling, but she tries her best not to make a habit of it. liberal with the block button, even with people she knows irl. every time Anne posts she replies with at least a dozen heart emojis

Elizabeth: 10/10. i feel like she’d try to be an influencer. makes a shit ton of “collab” videos with her dad and Mrs. Clay in Bath. she puts about a million things on her story every day. she likes to post herself shopping and tag the store thinking they’ll engage when it’s like. target

Mary: 9/10. she is forever watching those AI animal videos, thinking they’re real and sending them to everyone. shows her kids’ faces online despite her husband’s (admittedly very mild) protests. reposts stories about events she wasn’t at saying “wish I was there :(”

Charles Musgrove: 7.5/10, only because I think he’s slightly more online than Wentworth. spends a lot of time on twitter because Mary’s not on it and sometimes he wants a lil break. will use chronically online lingo around his parents and get blank stares.

Louisa: 8/10. TUMBLRINA. she has other social media but mostly i’m claiming her for us. blogs religiously about musicians she loves (mostly kpop), and her blog aesthetic is gorgeous. has many beloved mutuals that are extremely concerned about her TBI

Henrietta: 7/10. also a tumblrina but in slightly different fandoms. runs a pretty popular heated rivalry blog. she maintains Louisa’s kpop blog after her accident and does a pretty good job. feels obligated to reblog discourse posts she doesn’t fully understand

Mr. Elliot: 5/10. i can’t see him being super online. he does have twitter though, and he does call it x. very much enjoys using the internet to lie and spread misinformation. i think his most used site is linkedin. “this is what mr smith dying taught me about business” and shit like that

Mrs. Clay: 9/10. once again she likes to make tiktoks, with and without Elizabeth. “this is a day in my life as a widow with two kids” and the like. Elizabeth and Sir Walter make a callout video after she runs away with Mr. Elliot and she gets so much hate she deletes her tiktok :p

The Crofts: 4.5/10 as a set. they have joint instagram and facebook accounts and a joint email. they’re not super online though. Most of their screentime is puzzle games. he seems sliiiightly more online than she is though

Captain Harville: 2/10. he strikes me as really not online. maybe slightly moreso than he was before his injury, but he just doesn’t have that vibe to me. the only one that could’ve distracted Anne while Wentworth wrote the letter because everyone else was on their phones

Captain Benwick: 6/10. he’s a tumblrina too tbh. has a very cute blog that’s mostly his extremely sad poetry. he reads Louisa something he wrote while she’s recovering and she recognizes him as her mutual. this is far cuter than what happened in the book i think

Mrs. Smith: 8.5/10. would be far less if she could regularly leave the house. employs herself with puzzle games and wikipedia and likes scrolling through kitchencels and AITA. has an uncanny ability for finding the anonymous social media accounts of people she knows

bonus Dick Musgrove: mostly used snapchat. Charles deleted it off his phone after he died so their parents wouldn’t have to see all that

Sir Walter has a silver fox fan club and he's enormously proud of it.

Mr. Shepherd has one of those advice lawyer blogs to drum up business but it's not very popular