I wired 2 outside free-standing lamps, what size of switch do I need (15/20amp)? I wired my first 3-way switch and the light seems to work properly, can I assume it is wired correctly? Could an improperly wired switch or outlet in an electrical box cause a fire or would the circuit breaker blow first?

I replaced a (dual-switch) light switch that run two different lights in my kitchen ceiling and when I turned the top switch to the "on" position both lights come on instead of just one. The bottom switch doesn't do a thing when I turn it on. They used to come on one at at time depending on which switch I turned to the on position. I also replaced a (dual switch) that runs my outside porch light and inside outlets in the living room. Only the top switch works now when I turn it "on" and both the porch light and inside lights in the living room come on at the same time. The bottom switch doesn't do a thing now. Help. I thought I hooked them up the same as it was when I took out the old ones.