Switching to formula.... HELP please.

I’ve decided I need to go back on my meds, with that being said I HAVE to switch to formula.

I’m just not sure how it all works.....

1.

I’ve read some people use bottled water others tap, or filtered.... and some say boil for 2 minutes?? What’s best?

-can you use a brita filter?

-could I boil the water and then use the brita filter?

2.

Is it okay to make a whole days worth and use a dr. Browns pitcher or Baby Breeza pitcher and then pour as I need?

3.

Should I use RTF bottles until 3 months??

4.

When can’t you use already mixed formula anymore? Expiration? Hours? Days?

I only ask AFTER googling because I’ve read sooo many different things, I’m just lost and I want the best for my baby so I need to see what the majority of people do.