noob questions on unlocking and roms

[mtnbkr]

I just got a TP2 (i know, late to the game). It's on Sprint and brand new. I've been reading through the forums and searching and I've got a few lingering questions that I'm having trouble finding answers to.

1) Do I have to unlock my phone to load a custom rom? (I believe yes)

2) Does unlocking the phone cause problems for me if I have problems with the phone and want to claim warranty? Can you relock a phone then and pretend you never did anything?

3) Themes and roms confuse me a bit. I understand that roms change the actual underlying functionality of the phone and often optimize it. I also see that roms add some "eye candy." Can themes add this eye candy and offer the same user interface that a rom provides, but perhaps with a performance hit since the theme doesn't optimize the phone at all? Do people flash a rom then install a theme? Does the rom come with a theme? Can themes be loaded on any rom or only stock?

4) I also so threads on optimizing the phone and cleaning off the clutter. Does that really matter to me if I flash a new rom?

I apologize for the basic questions but I haven't found 100% clear answers and really need someone to SPELL IT OUT for me. Thanks in advance.