IIRC my radios are fused at 15A. Without consulting the manual 10A should suffice as 10A at 12V is 120W and a class C amplifier should do better than 37.5% efficiency. Rarely run at 45W but sometimes its helpful.
Do not have the upfitter switches. Was on my "desired list" but wasn't high enough to make additional effort to find a truck so equipped. Looked like $100 to $200 could retrofit the switches if needed. Don't really need them, only interested in borrowing power from where ever they get it.
For the hole in the roof my current plan is to disassemble the dome light so see if that will expose the structure and help indicate where it is safe to drill.