Soaking is not the best way to remove old hinges from cut squares. Use the wrong end of your stamp tongs, rub over the old hinge briskly. This usually loosens the hinge. In my opinion, a hinge remnant on a cut square is ok. A stack of hinge remnants is not. Mounts make for a nicer looking album page.
I have extra envelope pages for a two-post binder National binder in excellent condition. Pages go the the early 60s (1962?/Pony Express issue?) if I recall correctly. Just cover shipping. I'd rather see someone use them for mounting cut squares than see them cut into filler strips for my album.
I used some 2x2 coin pages for my cut squares. I had to add some thin cardboard (I cut up some comic book boards). Anything that didn't fin in the 2x2 I just cut the sheet sleeves a little wider to fit the cut square.