PS You can't really "min/max" in this-----*FAR* too much "randomness" & "luck" ----so a strategy that works in one run may not work in ANOTHER.
The reply been trying to give, is *ASSUME BAD LUCK* [so can't find item to buy; more likely char "dies" from fights; no or very few easy quests. (point of fact: With current bad design, all you have to miss is 1 or 2 *EASY* quests to wind up being stuck past D28!)
sidenote: you mentioned all *FOUR* Guilds---so servant too? (I think only gotten them to 500 *ONCE* before D30!)
One time even "sold" Daisy to meet their quest! lol What if you can't find the slave they want? [ex: ELF, 50 charm] not only do you need to BUY it, but TRAIN it!! Gold aside, that's not always possible. (let's assume bad luck----so several days to find/"buy", but FACTOR 2-----so *LONG* time to train! )