Its actually really easy, just need to know how the game works. You can have a mansion full of prostitutes and make the required money, you can also go the "fishing" method that people recommend here, but its even easier to use this "fishing" method to pay the first one, then before the second one sell fish to get enough money to buy the materials needed for the "Rough Wood" resource upgrade in the mansion (the store restocks each day). While passing days try to get worker outfits for each of your wood choppers as well as some axes and use the "Dates" to train their physic. More Physics = more wood. As they get exp give them any classes that give +Collection or Physic bonuses, and obviously when recruiting new people prioritize people with higher Physic. As it is right now I've just paid off the 2nd loan and have more than enough to pay off the third loan. By the time I hit the 3rd one I would have LONG since had enough for the 4th one.
The above is roughly the same for the 'prostitute' route just with a focus on charm instead. And if you want to go the fishing route, Wits is what you aim for. It'll show you what stat and item each job uses on the job assignment screen at the bottom. Just make sure you remember to sell the wood / fish before the loan day rolls around.