How do you start making enough money to keep up with the debt? I've tried having all hired help out mining while mc is forging swords to sell, but that only gets me past the first payment. Am I missing something?
You need to ruthlessly optimize for money produced per unit of time. The jobs are
not created equal in this regard.
Paying off the entire debt is possible, I've done it. You need to think like an evil bastard with a head full of half-remembered econ 101 lessons and a graphing calculator to the side of the desk. I'm not saying this is the only way to play the game, but if you like management sims, this is how you do it. If the words "hey hey, people" don't confer an instant Pavlovian response in your brain and if you haven't ever made a spreadsheet to optimize your gameplay strategy... maybe this isn't how you in particular have fun. But if that is your idea of fun, keep reading.
The market prices for resources don't fluctuate at all. Supply and demand no real, suck it, Adam Smithcels! Therefore, you need to be collecting the resources that are the most expensive per unit. Those take a little longer to collect per unit, but
only a little. Rough stone and rough wood are only useful inasmuch as they are crafting ingredients. Mining iron, or better yet mithril produces much more $/turn. Magic wood and ironwood are harvested only a little slower than rough wood, but sell for several times more. Make sure to give your resource-collecting slaves ranks in worker and farmer; the resource collection bonuses for those classes are enormous, and make sure to equip them with the correct tool type for the resource they're collecting (yes this is a pain in the ass and the interface is bad), because again the bonus is enormous.
It's always better to get guild quests for a particular resource than it is to just sell the resource on the regular market. The guilds are always willing to buy the materials they specify in their quests at a huge markup, possibly because they were born retarded and are unaware of the existence of the market. In fact, the markup is so large that in many cases it is possible to buy the resources off the market and sell them back to the guild and still make a profit. The profit from doing this is slim, but in some cases it's worthwhile because it means you get cash instantaneously and the completed guild quests refresh the next day.
The very best possible guild quests are the ones where they request resources that can be bought for guild reputation. This is because completing guild quests also gives reputation, and you come close to neutral on guild reputation and far ahead on gold.
The slave request quests are tricky. The low and medium difficulty ones are generally OK, but the high difficulty ones that request multiple slaves are 100% a player trap because the payout doesn't scale with the number of slaves requested. Again, these quests pay a huge premium over normally selling the slaves, so it's generally worth it to look over the available slave request quests after looting a dungeon to see if the slaves you've accumulated fulfil any of the requirements, as selling them through the quest system can yield a several hundred or even thousand gold bonus vs. quick-selling them.
Try to pair dungeon clearing quests with monster killing quests of the same monster type (e.g. kill x number of undead when raiding a crypt). The one-shot combat quests where you go to a single location are better payout per turn than the dungeon clearing ones because they only take on turn, while a lengthy dungeon can be a multi-day operation. The assistance quests generally have the worst payout because the time they take to complete simply can't be whittled down short enough with character skills.