By the way, my school doesn't offer Spesh because there aren't a sufficient number of students to open a class.. so I'd be forced to do it by distance ed and get a tutor. I'm already going to have Methods + Chem tutor and Medentry classes, so I'll literally have very little time to properly study... that's another reason why I don't want to do Specialist..
For picking subjects, I think ignoring perceived difficulty and scaling is probably the best approach. You'll be putting a lot of work into any VCE subject. Pick the subject that you think you'd enjoy more.
I guess it depends on your learning style, you don't really need a tutor to get through VCE. I found Distance Ed Spesh is excellent however. Also you don't need Unit 1/2 GMA to do Spesh - I can vouch at least that distance ed spesh doesn't assume that you've done GMA. I will also say that the distance ed spesh teachers are also excellent, and if you ask them for help they will help you a lot (whether that be by phone, email etc.). It does require a lot of self motivation, so if you don't really enjoy the content (enough to go out and read about it yourself), then I would be somewhat wary of doing distance ed spesh. You still do have to hand in work every week for marking to a teacher, so that might end up being motivation enough to do the work required at least.