New Cam

Ok as far as gas mileage goes I don't know but really if your modifying gas mileage shouldn't be a concern. Yes your car will pass emissions but to do this you will need a good tune, and yes a good tune is very important. Now as for gears you are going to need a chip to correct the speedo after the new gears and then if you get t he cam later you're going to need a re-burn. As far as the pullie and trans cooler sure go ahead but you should probably get a shift kit while you're at it.

Honestly if you really are willing to spend this much get P&P heads, intakes,and a cam. You'll feel those alot more and will cost you about the same as a cam and gears and t-lok. But hey do what makes you happy.

You won't see alot of power or a loss in mpg with a cam by itself. Once you start adding more stuff, the power will increase more compared to a stock cam.

I'd go with what cuban said, get port work done with your cam. You'll see some pretty nice gains from that.

Actually there have been 99+ cars with just a cam that have gone over 200+ rwhp with a now inferior cam. If I were you I would contact mikael at rpm-mustangs.com.