I'm aware this game is still in an alpha stage, but I would've hoped the default playthrough was at least playable until a certain point. But it's barely possible to make 1000 gold in the first three weeks, let alone 3000 more in the following two! And the fact it just throws you to the main menu, regardless of when you last saved? Who thought this was a good idea?! 

Just... rebalance this. Half the amount is more than enough. Heck, I still have no idea how you would be supposed to make 1500 in two weeks.

Oh, and while we're at it: The notice board quests? Not very useful when they require you to have stuff you literally CAN'T have by that point.

I have in multiple versions made more than enough money to finish the entire debt with little to no difficulty using the default start option, while using what is supposedly the slower method of making money (pure gathering workforce). The first time I did so it was a close call around the day 50 payment because I didn't have a clear idea of how to progress along that path yet, but the latter few times I have finished building every payment with weeks to spare.

I have not fully tried in the latest version yet, but I have made the 1k for the first payment in less then one week, so 3k more should have been easy by that due date. The main thing to note about trying to actually pay the debt is you should try to focus either full gathering, or full combat from before you even make your characters, the quicker you can get the rhythm the easier a time you will have. An important note; anyone you send to a dungeon, combat encounter, or noticeboard quest will not do whatever job you've given them at the mansion until they return.

As for the quests they are a bit difficult in the first couple weeks no argument from me.
The quest requirements can be anything from the tier you set them to for that faction, though they do default to the easiest tier of quests. You might not have the infrastructure to complete all or even any of the quests for a week or two if they randomly pick craft tools/accessories before you have the smith/tailoring upgrades, however you can buy items to fulfil the requests if you can find them in the market, the market stocks change daily, and some of the places you can travel to (mainly the locations that are only one 'turn' away) have markets of their own that also change stock daily.
The item turn in quests can be completed with things bought from the market usually for more than it costs to buy them as long as the reward is only gold and rep, if you have higher charm the rewards from quest will also increase.

I did it in the earlier versions by restarting until I get sub-quests I could actually finish. Then it's matter of not over-spending. The recent version should be even easier to make money, since you can just sell the slaves you got from dungeon for a sizable profit each run (anywhere from 100 - 900). Even if you're unlucky with the drop, you still shouldn't have to spend more than 3 trips to pass the first 1000 (Goblin dungeons are recommend, since they're the easiest one).  The 3000 can be bypassed with certain privilege that comes with advancing the main questline, or you can just pay them still; your combat party will have become strong enough to make several trips without resting by that point.

In my experience, an efficient way to make money is to assign one's first few slaves to wood gathering. Your characters will grow their physique stat the more they work, so if you consistently have them gather wood, they'll bring in enough funds to pay off the debt.

Well, I discovered it by failing, thinking about why I failed and trying again with a new strategy. Several times. Also, at first I attended to all the little hints and prompts in the game. Meet the guild leaders and get info from them, look at the  options for action and try them out. That's part of what makes a game enjoyable to me.

I've been starting with 2 half-kins usually wolf and cat. Both fighters. Usually don't get a mage type until I recruit Zephyra unless I find a too good to pass up mage type  in a dungeon. Also I build a tailor and forge as soon as I can. 

Dungeon diving and resource production. You can relatively easily pay off the entire loan (even the "impossible" 80k or whatever the final one is) by just gathering magic wood and mithril. Sell your excesses for massive profit. 

The first week is a bit of a squeeze, yes, but finish like one quest and go dungeoneering and you're fine. Dungeon crawling is the fastest way to level up characters to make them better workers. Slap work boosting traits on them later and they'll gather obscene amounts of resources. After a couple weeks you'll never need to worry about money again, and the only things you need are stuff like obsidian, iron wood, adamatium, etc. 

it doesn't work quite so good since the change to how levels work but there's a stratagem that reliably allows me to make the first two payments relying on two characters without needing to do rep quests or dungeons at all even, i call it the "Nearest Green Trick" inside my head, because it's just "make whiskey=> sell => profit" even if you have to buy grain

1) farmer slave - typically a human (dryads are better but rare spawns) slave with high phy, send them out to gather grain, get them the "farmer" job asap, make sure they don't have any negative traits that hurt farming

2) cook - usually an elf or (even better) a (half-)tanuki with high wit (and ideally the craft +20%" trait), park them at home and have the craft whiskey (set to infinite, and just drag an order for meat soup or whatever over the top when you want to stock inventory for food-to-use)

if your cook runs ahead of your farmer you might need to buy supplemental grain from the market, and usually by the time you can build the "gather grain" upgrade the farmer's obedience drain will be so slow you can probably just leave them deployed indefinitely

negative traits that affect other jobs (like that coward one that cuts hit rate 50% or the anti-sex ones) are actually good for these characters, because they lower the purchase price and are irrelevant to their jobs, so it gives your budget more breathing room to buy other slaves as part of the dungeon squad or whatever

there are variations on what you can do with the cook, "apprentice" is usually a solid move too because wit+10 helps with cooking & is part of an actual class progression tree to keep them useful after the first month, although "apprentice"+"cook"+"alchemist" is usually a pretty solid end goal for them because they can house-sit, making food or magic items, and then also use the apprentice hypno-magics to manage other, newer / less tame slaves; a peon usually works better than a slave for that later stuff, but it doesn't matter if the cook is a slave or a peon as far as this stratagem is concerned

although, that said, it is very funny that the prologue is easily the hardest part of the game, where you have to rapidly make decisive decisions so you don't get trapped in a doom spiral that sends you swirling down the drain to a game over, unlike the entire rest of the game where you can all the time in the world to progress a quest

Farm Mythril. JUST FARM MYTHRIL!

Mythril is not easy to come by in the first 1-3 weeks.  By the time it becomes easy to mine mythril you don't need to make piles of gold. At least if you are following the plot.