Is it ok to put a betta into my aquarium?

I have a 29 gallon tank,(I'm going to put other fish into it too.) I have white gravel, it's a rectangular tank, and a have a filter. When I look at it from outside(where I'm sitting) I can see the reflection. My dad says it wont see the reflection from inside the tank but will see the reflection if there's something black(the filter is black) next the the tank wall. I have no idea how black could affect the reflection, but I want to know because so far my dad is a failure at fish keeping.(he's killed over 50 fish). If I want this to work out I can't take answers from him >.< I also have currently a flame gourami and a goldfish. I just got them and the goldfish is pretty young/small. Also would the betta get along with a cherry/tiger barb?