Anguy won 10 000 golden dragons on the Hand’s tourney with his archery skills. If he had more modern-day senses and long-term thinking about his life (no offense, Anguy), then what could a man of the smallfolk have done with this amount of money to improve his life in the long term? What are the options?

Great question! 

I would say that his best bet for upward social mobility is to find an heiress of a poor noble family and marry his way into a title (either that of a landed knight or a petty lord) – the fact that he has a lot of cash on hand means that he can skip a lot of the steps along the way that people in medieval societies attempted to climb the social ladder. It would probably also help if he were to serve with distinction in war and get himself knighted* to belt-and-braces his drive for noble status, and given his superlative skills as an archer that wouldn’t be hard. 

* hell, he managed this in OTL (in a fashion) despite having wasted his money. If Ser Anguy survives the BWB, there’s no reason he couldn’t have a decent career as a sworn sword or household knight (and even a tourney knight, if he can find enough tourneys offering archery prizes). 

Next best, he could marry into a merchant family. This would advance him up to the status of burgher, and I would imagine there would be a lot more merchant families who’d be quite happy with such a large injection of capital and who’d be much less snobbish about his background than the minor nobility would be. My hesitation here is that, while Anguy is a perfectly nice young man, he doesn’t seem to have much of a head for or experience in business. Might be happy as head of security, maybe.

Another possibility is creating a sellsword company; he certainly has the up-front liquid capital to hire several hundred skilled archers and sell their services. Again, I don’t know necessarily that Anguy has the necessary head for military command or small business management, and mercenary work has all of the risk of social mobility through military service with less of the possibility of advancing into the nobility. Also, it would probably mean spending a lot of time in Essos, and Anguy might not like living abroad.