Do minor quests for local nobles and hunt down bandits at every single opportunity you can get. I really can't stress hunting bandits enough, not only does it net you new equipment and money, but it also levels up you and your party too so you can eventually start winning those tournaments.
As for what to do with that money, I recommend choosing a city/region as your home and start buying acres of land to generate coin for you. Once you have enough acres, you'll easily be able to pay for your troops' upkeep and then some.
Ideally, you should have joined a faction by now and earned a village for yourself. In which case, develop the village and do as many quests as possible for it since high relations net you better taxation and troop recruitment.