Planning 6 mos in SMA- what do I need?

The tourist visa is called an FMM and can be for up to 180 days, so ask for 180 days. There is a minimal cost for that. I don't know if you can get the full 180 days when applying online, but I was able to get one for less than a week with no problem. Note that you have to apply for it within 30 days of your arrival in Mexico:  https://www.inm.gob.mx/fmme/publico/en/solicitud.html
Otherwise, it's fairly quick to just get it at the border.

I assume you'll be renting a place down there, so bring pesos for most or all of that amount. You can get cash at an ATM down there, but make sure your bank knows you'll be down there. It can also be a good idea to have more than one ATM card.

I don't think you'll need bank statements. If you're willing to pay rent multiple months in advance, that will make any landlord happy, but I have not specifically rented down there.