The first thing to consider is where you would play your home matches. Private club? Public courts? Whatever you come up with, you should hang out around those courts and recruit players that play there regularly. At the 3.0-3.5 level, there should be more players to choose from that at higher levels (4.5-5.0).
Usually costs are shared among the teammates. Tennis balls, court fees (if applicable), and food/refreshments for home matches.
Instead of starting your own team, you might want to consider approaching an established 3.5 captain in your area and offering to be an extra on his roster. You wouldn't expect a lot of playing time, but you would be available in case he's short on players. And you would get to practice with the team and establish yourself with them as well.