You can get your AA degree on your way to your BS, or you can go straight for the BA – you will take mostly the same classes the 1st two years. Either way, it will take you four years to get your BA.
The cost is very different – you can earn your AA at a community college at far less expense than spending the 1st two years of college at a 4-year school. Your AA is transferable to any 4-year college.
Some people like the feeling of graduating after two years – getting that diploma – then going on. Some prefer community college the 1st couple of years because they are usually quite a bit smaller than universities or 4-year colleges.
A BA in psychology is worth very little. About all you would be prepared to do in the field with a BA is intake. It takes an MA to be allowed to be considered a psychotherapist of any kind.
