1. I think it depends on the person, As soon as I got Blazblue I jumped in with Carl and sat in training for a good 90% of my time during the first two of weeks or so. So no you don't have to change if you don't want .
2.I'd say about a week and a half, just messing around and testing stuff out is a nice way to learn
3.Analog is fine for now, infact I'd suggest you stick with the analog, then when/if you decide to play competitively switch to a Fight stick.
4.Carl only combos first, then practice using his 6D in ground loops, then try to mix up the ground loops by learning Alle-can~.
5.Not really, It all depends on how dedicated you are :3, Messing around in training mode is the best way to learn in my honest opinion.
Hope that helped~.