How many credit cards should you have?

Ok. I'm in the process of rebuilding my credit. I currently have 2 secured credit cards. One has $500 the other $300. I charge $20 on each and pay off in full each month. My question is, should I get another one and do the same or add more money to these two? How long does it usually take to see a dramatic increase in credit score? So far my TU has jumped 17 points and EQ 13 points. I have only had these cards a couple months. I also have 2 installment loans always paid on time. Any suggestions on what else I could do? Thanks guys!!