Im pretty sure -SPOILERS- will come back as a ghost. It already happened with -SPOILERS IF YOU THINK TOO HARD-
Doubt it. Those ghosts trained to become ghosts during their lives (besides one though, which is kinda odd). SPOILER didn't train and also wasn't force sensitive. They're force ghosts, not just spooky afterlife ghosts.
The SPOILER actor also didn't show much interest in staying on.
I really enjoyed the film. They leaned heavily on the Ep 4 parallel's, but that's not an issue to me, unless 8/9 show great similarity to 5/6.
The films were well made and well acted. They were exciting, pretty, funny at opportune times, and genuinely fun. The new things we got to see were great, and it was a pleasure to return to some old things too.
It's petty to describe 7+ as just being a grab for merchandising, as Star Wars merch has never stopped being produced/bought since Star Wars hit screens. Plus, every Star Wars from Ep5+ has been met with substantial amounts of merchandising being pumped out.