Side activities need to make sense, wood cutting and mining take way too much work for almost no gain, you could just buy some from merchants or get a TON of more orens by actually being a wticher.
Horse racing you assume its some kind of pointless side activity, however, I bet horse racing can be pretty important in the lands of Novigrad where all the nobles live and constantly make high bets, whether of money, possessions or favors. Also a horse race takes little time and effort compared what you mentioned.