#2
micing your instruments actually makes them much clearer. assuming you record in a quiet room. otherwise, that toneport should do fine. And IMO you may only need a mixer if you want good production, and maybe you needn't meddle with one when doing amateur recordings.
#3
if you have a toneoprt you dont need any mixer.

the only major time a mixer is needed is if you want to record with an analog setup and you have loads of money to start with...

You are still running though Gearbox with a toneport. I suggest a new interface and to mic your amp. The toneport interfaces are not all that great and the amp/preamp models in Gearbox dont sound all that good either...