What is hammered metal Pittsburgh paint - I just know the rustoleum spray hammered metal which wouldnt look so great on walls + the high sheen would only emphasize the roughness

Im not sure I agree that prepping walls for regular paint is too much work - why would it be more work than prepping for the hammered metal (whatever that is).

Assuming the old wallpaper paste is gone and no major cracks or fallen plaster to repair.... all you need is some good non shrinking spackle and/or finish plaster to even out the unevenness and/or fill in minor cracks and nail holes. It won't be flat like drywall. 100 year old plaster walls are allowed to look a 100 years old! That's part of their charm. Then use Zinsser Gardz as primer (seals highly porous old paint including calcimine which is the worst of the old paint) , then top coat in flat or maybe matte, nothing with sheen that would emphasize roughness.

-

Previously wallpapered walls can be the devil to paint. Because residual wallpaper paste interferes with the adhesion of the paint. That is why using Gardz is important. I would clean the walls and roll on a coat of Gardz before making repairs and then another coat of Gardz after the repairs are done. Gardz isn't super cheap but it isn't all that expensive either. Cheap insurance, IMO.

And, yes, don't strive for perfection. Old plaster is allowed to have some flaws.