That sounds good. I could cut 2" rectangles in some Daler board and get that framed.
So you can get 2x2s to fit a farthing, halfpenny, florin, etc? I can see that these things will usually be sold in quantity and that if I only want one of each .. But if they are mounted side by side the cardboard will probably not quite match if they are made by different makers.
Are coins a tight fit in 2x2s? Do they rotate?
If you buy a coin from a dealer, how is it usually packed? (When you start thinking about something new there are suddenly lots of questions!)