Biab for dummies

Hey all, I've been reading past threads that are several years old at this point, and I've found a few that come close to what I'm after. None that explain it from scratch though. I'm an extract brewer trying to get into biab. I've been collecting supplies here and there as I find decent deals or I have the money. Now I'm trying to really get a handle on biab processes. I've seen a lot of posts on how to do it, and even more different answers with different processes. I understand everyone will do it a little different, but what I don't understand is why, or what the difference makes. So basically I'm looking for biab for dummies haha.

A few questions or inconsistencies that keep coming to me:

Biab 3 gallon full boil in 5 gallon kettle, or 5 gallon partial boils? (Limited to brewing inside on a stove with 5 gallon kettle)

Heat the strike water for the grain, add grain to the bag, then do you remove the kettle from the burner and cover it? Wrap it in a blanket? Leave it be? Leave it on the burner but keeping the temperature constant?

False bottom in the kettle so as not to burn the bag necessary?

Sparge or not to sparge?

Mashout or not to mashout?

I'm sorry I know this is probably fairly noobish. I'm hoping there are others on this forum that have similar questions to these, and maybe this will serve as a more updated biab explanation post.

Big thanks to everyone on this sub!