ToA wiki has explanation on what different Stats do, it also has Achievements page that tells you how to easily edit achievements if it seems bothersome to farm them.
About Charisma, I usually take either Charisma or everything else for a run. If I play with high Charisma, it's either the character that won't be leaving the first location, or I actually get 8 Charisma in the very end (it's possible with other stats still high on high level and using additional charms and a little upgrade). Then I can return and get me companions.
Stat equipment isn't costy. It's helm for 25, heels for 25, gauntlet you can find, or it will be additional 50. And you get +1 Perception, + 1 Agility and + 1 Strength. Must have. Also really great armor is around 400 or 350. Reinforced shield is 50, Broadsword is 50. And after that you're unstoppable with adequate stats.
If you can't beat Quetzal, well, your character is weak. She actually is a low tier enemy. With efficient build she can be taken out with 0 things bought beforehand. Even without farming achievements, if you're precise. With many achievements farmed you can have plus 100 gold or so to the beginning 50 by default, also more stats and perks. You get some money from Brothel, and it really all goes in breeze.
Also you can steal stuff. With Agility around 8 I wouldn't even bother spending 100 for a weapon and shield, just steal. And if it's lower, you can steal Cat Potion from General Shop and Strange Merchant, it will temporarily give you +3 Agility. With 12 Agility I can steal 400 gold armor. As you can see, there are opportunities to make life easier if you look for them. Some of the info can be found on wiki.