Your post is kinda all over the place but I'll try lmao.
So in my first run I went Fairy for the MC, 1st slave was a Wolf beast person. 2nd run the MC was a Fairy, 1st slave was a Dragonkin (this is where I found out there were other hidden classes). It should be noted that for my first run I never bought any gear from the shop AT ALL, never had the spare money to cause I didn't know what I was doing. The only upgrades I took before dropping the debt was Tailor, Smith, and Alchemy. Alchemy ended up being completely a waste since I didn't know where to get the mats for it at the time.
Also the Dungeon quests can be cleared with JUST your fairy and 1st slave, but you need to take archer first for your slave, and also go very slowly till you can get some gear drops from the dungeon or at least until you get a healer class for your fairy. Bear in mind, this is what I did on my FIRST playthrough, when I had the roughest time and had no idea what I was doing.
By 3 debts I mean 3 debt payments. The payment on the 14th, 28th, and 50th(?) I think.
Taking anything below good growth is fine for a slave you don't intend to keep, or if you just need one temporarily.I agree that some of those quests need to be rebalanced though. Getting 2 "clear dungeon" quests first thing is annoying.
Like I said, I barely touched upgrades at all on my first character before the debt was cleared. Oddly enough my unarmed Fairy healer, and slightly armed Wolf Beastkin archer, were able to take care of any Slay quests, Dungeon clear quests, or beast hunt quests. After I figured out Mithril exists and was able to mine some to make heavy armor for my beastkin those quests were a breeze.
Yeah my first and second run was the difference between night and day. My first quests were all "slay wolves" or turn in 10 cloth. Easy stuff.
The version I've been using for my hooker run was the current one (at time of posting) I was able to get enough money to pay off 2 debt payments within the first 7 days or so days. The only hard parts were doing dungeon / slay quests with a group full of hookers, and getting materials beyond basic wood and stone. After I got the Incubus / Succubus class with the charm ability I was able to actually go in dungeons despite each character having only hooker classes. I never would have set foot in a dungeon if the fighters guild would stop giving me ONLY those quests for 4 weeks straight. I haven't tried the full fishing build yet, will probably try it next.
Edit: Also make sure in the beginning that you only use the "train" option when using the date feature each day. Getting those early stats quickly can make all the difference for any run, but especially so in the hooker run.