https://imgur.com/a/YtRLzFy

Not to harp on about it, but I decided to see how far I could get with steamrolling the rest of the map just off my cash reserves. This is the furthest extent I can get to before going irreversibly bankrupt. The main issue I see here is that even if I were to disband every soldier in my kingdom, and have no standing army, just the maintenance of my empire alone would exceed my total revenues, and with no one left to trade with this represents an irreversible and irreconcilable financial collapse. In this screenshot it still shows 3k trade income because I'm not at war with the Normans yet, who own a couple provinces mostly in Kent, but if you take that away, my total income from all territories with maxed out economy buildings is 5,283, and that's with a "high" tax rate active, while my empire maintenance alone (not army upkeep) is -6,222. So it seems that without multiple trading partners it's actually impossible to keep your economy in the green even with 0 military units in your entire empire, or am I just missing something?
Anyway, love the mod overall, this mod alone make ToB one of my favorite tw games, and it keeps me coming back to it, so I dearly hope work will continue on it, I just think either I'm missing something crucial about how economy works in this mod, or the economy has some serious oversights in it which make it ultimately unfeasible past a certain size.

Edit: some additional details on my maintenance expenditure

Okay I'm embarrassed I keep adding more to these posts so I'm done after this, I promise haha. But I thought it was important to add some detail about my maintenance situation, as it relates to the overall point about the economy systems of the mod. In this campaign, out of 47 provinces owned, I have 11 Master Bard's Halls, which makes up the lion's share of the maintenance at about half of my total maintenance upkeep, the rest is spread around estates, a couple of round towers, and libraries (which I can probably just deconstruct now that the tech tree is fully researched). I don't build any churches outside of special regions just because the maintenance is too high, but as Wales bard halls are just too good so I get as many of those as I can. Anyway though, the problem as I see it isn't that maintenance is too high, not at all actually, it's just that my base economy seems really really weak. With all of the industry and agriculture I have, I would expect my domestic production and internal commerce to be quite high, after all every tech is researched and every building is maxed out, my population is booming and everybody is happy, but it all amounts to a true pittance in the end without the possibility of trade. So I guess I should rephrase, it may not be impossible to have a solvent economy without trade, but it means having almost no army and virtually no buildings which cost maintenance, and even still it will be weaker than it seems it ought to be for such a large and well developed empire.