Pretty much so. Looking at your bike from the rear, you'll see the wheel being mounted between two vertical plates. The plates are the dropouts, and the distance between their inside faces is the dropout width.
The inside faces push against parts of the hub referred to as the locknuts, which gives the corresponding hub measurement of O.L.D. - Over-Locknut-Distance.

I'd say we don't know that yet. Installing a rack, replacing a rear wheel and a brake isn't exactly rocket science and well within the reach of home tinkering for someone with a bit of basic skills.

If you say so. I haven't had any need to do any research so I really can't tell. There's probably a way to make it work well enough.

Why not post a few left-side pics? That way, we'd have a better chance to judge what it'd take to transplant your drive to another bike.

It might be bolt-on to almost any frame, or it might require a specially adapted frame/dropout.

Again, there's really no telling. If it is a straight swap, I'd guess at 1-2 hour's work of moving parts over and installing the rack incl tidying up cabling and such. If it requires serious rework of the frame, then it can quickly become expensive. But if it is a straight swap, then it's comparable to perfectly manageable bike-DIY tasks.

Well I' can tell you straight off that the Montague is the best folding bike I've tried so far. There are others that are "good, considering", but you'll never forget that you're on a folder.