#kykar

No, this doesn't work.

While you're allowed to pay the costs of a spell in any order (barring rare exceptions), you have to generate any mana you want to use to pay for the spell before you start paying costs.

No, you can’t.

While you are allowed to pay the costs of a spell or ability in any order, you have to generate any mana that will be paid before any payments are made. This means that any spirits you plan on sacrificing for mana will be long gone by the time you choose which creatures to tap for Burn at the Stake.