Regarding rubylith...
Although it is easy to find large rolls of rubylith for sale, it has become very difficult to source small amounts of rubylith.
I used to get mine from Dick Blick but it seems that they are no longer carrying it.
I have this (
https://shop.archsupplies.com/products/rublylith-masking-film-20x24) in my notes as an alternate supplier but I have never ordered from them.
A small amount of rubylith goes a long way in my practice. Although I will admit that I don't use masks all that often. Generally, I just go with raw, random edges when I coat paper.
If I don't want the uneven brush strokes to show in the final presentation (which is the majority of the time) then I use a mat which covers cover the edges when I mat the print.
Pretty much the only time I use masks is if I am printing for a folio where a set of unmatted prints are place in a folder. This is pretty rare in my practice.
I never remove the rubylith from its backing... there is no reason to for alt process masking unless you make the same size print all the time. Then removing the backing and adhering the rubylith to the glass of the print frame is quite convenient.
I just keep a number of 2 inch wide strips of various lengths around. I use transparent tape to construct a rectangle of the desired dimensions from these strips. It is easy to deconstruct masks made this way and thus reuse the rubylith.