If going square taper, I usually take a try & see approach. It can be fickle. The crank has an offset of whatever amount, the bb is of what ever length, the q-factor is what ever length, the derailleur has it's range. It's not hard, it is just fickle.

When it comes to any project with external bottom bracket cups, I just buy a crankset that matches. It turns out golden every time. Anymore, my goto is the used bike shop before any place else.

Looking forward to seeing how the project proceeds.