I have inspection coming up this month, and I have an exhaust leak right before the muffler. I plan on going turbo in about three months, and my question is should i just get a 3" custom exhaust from the cat back now and deal with the power loss, or just fix the pipe. And, how much tq. will i be sacrificing if i do get the 3"?

go to an autoparts store. They have this silver stuff in a tube that patches up exhaust leaks. Might help you pass inspection.

Patch the hole if you can, take it to a muffler shop and if it is too bad they will want to replace a section of your exhaust. If it can not be cheaply patched I would go ahead and get the 3" setup.
I can't tell you how much you will lose going 3" but it would be pretty noticable at low RPM's.