Tunes ? Who what and where for an '08 GT

So, Tunes are new to me. I'm building a 08' GT and need to learn..

Should I have the shop who is going to install my gears provide and install or should I buy them from Bama? If not Bama, then where? Whats your experience?

If I have the shop do it, can I add tunes from other sources? Would I even need or want to do that?

Are there sites that offer downloads to a tuner that work well?

If I buy the the tuner from the shop, can I add my own tunes later?

My goal is to add 3.73 Gears, A JLT CAI and Cams.

Thanks

thanks 90SF they are quoting a SCT X4 7015. If I need a tune later, do I have to go back to that shop?