Welcome to AF!!!!!!!!!!!!!
you picked a very awesome phone. it is good to see that the og evo is still considered relevant now in this day and age where bigger it better with the s3/s4 and the note 2.
the guides that mikey linked would be the one you will need. please read, read, and read some more. one thing though is if you have questions on boost then i would post in the boost guide. we have a few awesome guys who have experinece with flashing the phone to boost. they have subscribed to the thread and will be alerted to when you post a question. i do not know much(if anything) about how to flash a phone to a different carrier so i can't help you out in that arena, but the guys there in that thread now their stuff.
everything else though, please feel free to ask here.
good luck!!!!!