1) CDMA TP2's cannot be unlocked as of yet, I know that the community is working diligently on it.
2)You can't "clear" the ESN, it's the electronic serial number unique to each phone, it's kinda strange that you're able to find one used already, what you should check to see is if the phone was reported stolen, so basically you need to call your carrier and check to see if you will be able to activate that phone on their network.
Here's a relate post on another forum (mostly regarding a sprint phone but same idea)
3)You can install just about any app you want as long as it's compatible or signed *scratches head* I think there's a tweak cab file on ppc geeks that enables unsigned apps here:
4)Yes, not sure what the button combo is for sprint but for my verizon tp2 it's
-make sure the phone is OFF
-hold the "volume down" (the button on the side with the "-" on it) AND the send key (green button)
-While holding said buttons, press the power on button (red button) and follow the onscreen prompts.
5)It already is.
6)You can always disable Touch Flo 3D from the Today options or even install SPB Mobile Shell (I think that's what it's called) for a different theme, but if you're just talking about normal windows mobile 6.1 today themes, just disable Touch Flo 3D from the today menu in your options screen (All settings) and install themes you normally would as with any other version of WinMo 6.1
7) Phone works best with a good data plan and just like any other windows mobile device, expect to do a soft-reset every other day. And be ready for people asking you if you got a new type of iphone or that IS an iphone or if your phone has anything to do with the iphone.