The answer to your first questions; The amount of coins you earn depends on a lot of factors. If you play in tournaments (online or offline), you will earn coins for each match and if you win the tournament. You can earn coins playing matches both online or offline as well. The amount of coins depends on the level of your opponent. If you play a 1* scrub team with a 5* elite team, you will earn fewer coins. If you play a 5* vs 5* team you will earn more. You may also earn coins by selling players or discarding them. The level of the player depends on the amount of coins you receive. Most lower rated gold players net 300-320 coins. The inform players get you closer to 1000 coins if not more, but it is very rare that you would discard one of these players. You would likely sell and net 20k+ coins.
To answer you second question; You can build as many teams as you want. Currently I have an EPL - non-English team, an English only EPL team, a silver EPL squad, and a silver npower Championship team. I also have a USA team. All but the non-English EPL team are full (only 5 positions left to make it completely non-English.
Once you play more and more and buy packs/start trading your team will get better and you'll be able to play tougher opponents. Good luck and enjoy.