Hello, well for starters, you'll need to unlock your phone following the instructions
here. Once you do that, you'll be free to flash any of the ROMs in the
CDMA subforum. Just try as many as you can until you find want that is just right for you.
About activating with Verizon, well it depends, if the phone already has the VZ logo on it is almost safe to assume they will activate it. If not... well it can be hard since they have a list of approved phones based on their ESN (same as Sprint).