From Homebrew and Emulation you need 1.50 firmware. The 1.51 and 1.52 firmware you can get emulation but not homebrew (someone correct me if I'm wrong).
Supposedly newer boxed copies are shipping with newer firmware though I haven't read any reports of any coming with 2.0 out of the box yet.
You'll need a 1.50 bios (all-but unavailable to purchase from any store nowadays) in order to run anything but the games you're supposed to run. Sony started shipping 1.51 and 1.52 bios a few months ago, so odds are you'll be finding one of them.
I did remember reading at one point you can look at the console's serial number (visable through the box opening) and determine if it's one of the golden 1.5 consoles, but I don't remember where I found it anymore.
However, all is not lost - there are reports of a group that's been able to dump a 1.5 bios into a 1.51 or 1.52 console (NOT the 2.0 version that you can freely download on Sony's site). Rumor has it though you'll need another 1.5 console in order to do it though (it'll transmit the bios via the wi-fi). BUT - as of right now, it hasn't come out yet. It's expected soon. I'll report more on that when it becomes available.
Keep in mind that some games might force you to upgrade to version 2.0 in the future. As of right now, no game requires a bios upgrade in order to play, but it's expected to do so in the future. So keep that in mind for down the road. Emulation and classic games, or PSP titles. I do expect the hacking community to find a way around that code in the future, so time will tell.
As far as games go - you'll need far more than the default 32MB stick. Get a 512 or 1gig, and you'll be fine. And Sam and Max (talky) is all of like 70MB or so, if I remember correctly.