So I think as it's described cash is not really going to be the limiting factor for the First Order. It's started by essentially a bunch of Imperial Moffs and upper officers who fuck off to the Unknown regions - and as we saw in The Mandalorian this sort of person was rich. Even if Imperial credits don't spend well anymore, they've probably got beskar or other precious metals. Palpatine is also secretly backing them, and he's probably got entire rooms of money, as are a number of major industries in Republic space - at least per wookiepedia, Sienar Fleet Systems and Kuat-Entralla Engineering (the leftovers of Kuat Drive Yards) were secretly backing them and supplying them with material. They are not cash strapped.
What they should be is manpower and industry strapped. And the First Order's way of getting their army is the most expensive in terms of manpower - in order to get more manpower in stormtroopers, they have to spend it raiding outlying systems and presumably occupying enough to go door to door. They also have to conceal this from the New Republic, which means they can't hit anywhere too big or too important. They also can't bank up for a big order of stormtroopers all at once, or get new stormtroopers on short notice if they need them.
Like, near as I can tell, the First Order was supposed to have taken over the galaxy. That means military occupation, at least in key areas. And their ground forces for doing this were their stormtroopers - so the ones they abducted 15-40 years ago, back when they had virtually no presence in the galaxy.