Intelligence 2: While not as dumb as the proverbial doorknob, you are definitely what they call "slow." It will take you longer than average to learn most things. You can learn magic, but you will never excel in it. And most people will consider you a moron, because... let's face it... you are one.
- from the FAQ section
It looks like we don't currently have a write up for the Merchant/Business skill on the skills page. Like most practical skills, though, I imagine it would be tied to intelligence. Also note that "basic math" is part of the scholar skill, so without some education, your character will not have the skills to run a business. He probably has no clue what to charge for his services and will make up a random number that "feels" right to him or go with whatever people offer. But he won't have enough knowledge of the market economy to understand competitive rates or skill valuation much less cost-benefit analysis. He probably shouldn't handle his own business, since his best option would be to find a business partner who could handle the money and contracts. Especially if there are contracts; your character can't read, and legalese would confuse the heck out of him. But it's up to you how trusting you want to play your character or how aware he is of his own limitations. Just keep in mind to play your character at his intelligence level, and it could be very interesting.
As to learning scholar or business skills, it's not impossible, but it will take your character a lot longer than most. And he'll be more likely to learn things in a very simple form or things that get repeated often. So he can learn to count money, but adding large sums may always be difficult and time consuming for him, and he always does it by following an exact procedure that he learned. Nor will he be able to advance far beyond the basic level of skill. Again, a lot of it's up to the way you play your character.