I don't get notified of new posts in this thread and it irritates the hell out of me.. sorry if I have left anyone hanging.
I made SMBC with immitation vanilla once.. and ONLY once.. that stuff is soooooo nasty (sorry if you like it, but I thought it tasted like a big chemical cocktail and NOTHING like vanilla). I will never again use it.. ever.
I have never used shortening in SMBC.. but if I had to I'd use the high-ratio.
You can use gel colors.. they just tend to look grainy. It won't change the consistency unless you use a LOT. I tell customers that if they want bright dark colors I will use fondant because no one likes to eat black icing or red icing or bright blue icing. It stains your teeth and makes you poo a rainbow.
I do leave cakes out after they are covered in fondant unless they have something that needs to be chilled as the filling.
I know I missed some questions.. I will make sure to check this thread more often since the e-mail alerts aren't working on CC right now.