Lots of questions RTW. Smarter guys than I can answer them all here. but I'll take a stab at some preliminary answers.
To begin, your modern built AYAs will be fine with whatever you want to shoot. Personally, even in modern built guns I try to go for low recoil and seem to get about the same results as with the big recoil stuff.
The 2.5 English boxlock will be another matter. Depending on age mostly you have to worry more or less about pressure damaging the frame, recoil breaking down the wood. I'd stick to low pressure (RST) 2.5" loads in that gun if I were you.
Damascus barrels are whole different kettle of fish. Many of us here admire them and shoot them as well. The shooting of course is dependent upon barrel condition. That would include wall thickness, dents, bulges, and pitting. I usually do not shoot Damascus barrels in poor condition with any load...Geo
