do i need more than 3 characters?

if you can change classes at any point then i just need 1 character focused on physical one on range and one on magic right? then switch among the classes focused on those stats right?

You could get by on a single character, but the issue is you only get 1 mag per character. The most you can get for free would be 3, since you can create 3 characters. If you wanted to do everything for free, then yes creating 3 characters that specialize in an area would be best. Or you could spend $6-9 and get 2-3 more mags to raise on a single character.