I'll get to the Franchaela of it all first, if that's all you're interested in. Do the following if that's all you want.
Watch from season 3, either all of it or jumping around looking for the scenes with Francesca in it. Michaela is introduced only at the very end of that, scene with her in a black dress.
Watch season 4, same thing, Michaela has more of a spotlight here. I'd recommend watching all of it since the writers did a good job weaving Francesca's subplot with the main plot, also because Benedict (Francesca's older brother) is queer as well and might become an important side character in season 5 because he shares that with Francesca and neither of them know yet, but it's just my preference.
Whether you want to watch it all from the beginning or not, a couple of good things to keep in mind are:
- the show is more of a regency uchronia (alternate history) sort of thing, so all the poc people in positions of power are explained that way, the Queen Charlotte spinoff explains that aspect and is all around a really good 8 episodes, the romance story is very powerful from a human perspective
- the show still has some significant and hefty aspects of a regency setting, as in women debuting and having to marry and bear children in order to have any relevance, if any, inside society, so despite not being historically accurate it has very foundational setting aspects of that era that are necessary to hold the plots together, women especially have to live in that reality and watching the show with too much of a modern eye ruins the experience
- the love interests are all kept from the books, so I don't recommend investing yourself emotionally in headcanons and ships too much, it's still a very loose adaptation of the books' main couples, Michaela is the only expection because her character is male in the books and the showrunner and the network signed off on the gender swap with the approval of the original author
- It's not at all a thought-provoking show or anything, it's quite campy and light, taking it seriously is really not the point in various instances, but the many points of focus are emotions, love, family, remembrance and identity, I literally watch because the Bridgertons are a family of idiots and I love them, it is my comfort show because of them
- No matter where you start watching, there's a bunch of subplots that get resolved inside their respective season with a few exceptions, just a plethora of amazing female characters and friendships that are very enjoyable (getting emotional because of two women being just really great friends, it's a whole thing)
- Prepare for the string covers of modern pop songs used as music in certain scenes, they're actually very good, the whole soundtrack is quite nice to listen to
That said, do whatever you wish to do, regardless I do hope you have fun!
P.S. You can skip the sex scenes, don't worry about it.
