Recently, a couple of actors added extra postage for me, which was really nice.

Thanks, hopefully it works out :-)

2x Global Forever stamps stamps should be fine

I am in the UK and always use 2 of those (or 2x $1.05 before they changed to GF) to get my envelopes back (C4 with usually one picture).

I use 3 for Playbills which are much heavier and they always get back to me fine too.

I sent a letter to the US from the UK (paid at my post office so it should get to them fine). My worry is thate the SASE which I sent was C4 sized I believe, and my concern is that it will have problems getting it back. I have it 2 international forever stamps, and it should be under 2 ounces (2 small pictures, maybe a third if they add one, and the envelope). Are the USPS going to cause me problems. (Also I put a return address on the SASE, but I doubt the celebrity would pay any excess)