Do I need to unloack before flash

[mak101]

I have sprint touch pro from last 6 months but I have not tweak anything on phone, but after visiting the site, I am preparing myself to flash first time. I am trying to gather all information before flash it but I am confuse about unlocking phone. Do I have to unlock my phone before flashing any ROM?

And I see lots of ROM for my phone, is there any place where I can find any comparison between ROMs? Being first timer, what do you suggest about ROM, which ROM I should use? I know there is tons of information but difficult to find one.

I appreciate your help.

Thanks.