IMO a 76 IS large for a 4.6 at less than 1 bar. However it hurts nothing. If the exhaust side is small it will still spool reasonably. 10psi from a 76 is fine. ****** will start giving you issues between 10 and 12 however, so make sure your tuner has experience in tuning automatic fords so they know how to get the shift and timing tables at shift points to keep it together.
As far as intercooler, first get something that you can fit where you want to put it. In all reality one of the 24x12x3" cores from cx racing would be more than sufficient. If you want a better quality unit precision, spearco, and griffin all make quality ICs.
Meth in istself isnt bad. The issue with it is you can run out and at the worst time at that and if you have tuned around it, this can be catastrophic. You can have lights and buzzers but that is no guarantee you wont run out or a nozzle wont clog. You have added an active mechanical device to do the job of something passive. Meth has its place, especially when you are trying to squeeze every last bit out of a given octane and dont mind the maintenance. For your case, I dont think it is necessary.