Lookin really goog Paradox. The system seems like it could once again make the Africa Race more interesting, as lesser powers (nations ranked 9-16 who can colonise) can grab up the gold producing provinces to catapult their way to GP status.
Oh, and the map is beautiful!
I think you mean Colonial Powers (it's Great, Colonial, others, plus the unciv/civ split).
I was a bit nonplussed about this DD at first (like I've been about the last two as well), but this really seems like a good way to add some money to the system so you have reasonably stable purchasing power per capita (globally). Also adds interesting tactical choices regarding warfare.
Railroads are a bit tricky, but if there are money-only aspects to capis (or you for that matter?) building railroads and factories, I'd divide it probably first to unemployed people in the province/state (if there was a big building boom, even the unemployed would find some work occasionally instead of starving, then to all poor people in the province/state (1 unit of a POP is more than 1 person, the others would pool in for the extra labour).
As for founding regiments, you could have any money component going to your soldiers and officers. They're going through more intensive training and work than when they're just reserves (ie. manpower available in the province as soldier POPs, but the province isn't maxed out on brigades). For building ships, just officers could be enough, or just a different ratio for how much officers(aristos in early game?)/soldiers get.
Some sort of money-division script does already exists, since that's how factory POPs get their income (and aristos from RGOs presumeably).
I have less of a problem with no railroad maintenance, since they also don't create a profit. I suppose it could be theoretically possible to have an automatic "railroad company" factory for each state that employed some people like a factory (exactly like a factory), but just boosted efficiency instead of producing any goods. The problem here is that that factory would need to make profits somehow: possibly you'd need to have the factories and RGOs in the province paying the railroad company to represent cargo fees and tickets, etc. etc. One big problem is that for the different tech levels to make sense, you'd need to have flat efficiency boosts, but for the amount of employees in it to matter, it'd have to fluctuate.
It's just a whole new thing to code and balance without really any meaningful (in my opinion) game effect. Basically it's been simplified out on the assumption that railway maintenance (and wages etc) = railway revenues, and Capis will build them to make more money out of their factories. The player will build them (under planned economy at least) for the same reason.