I think it's impossible to predict how many titles there are going to be, and how long it'll take to complete - if they ever finish them at all. The ending of the first part basically confirms they're going to make a up a completely new story from here on, and since they don't even have a speculative outline it sounds like they'll be making up that story as they go.

I don't believe there was ever a serious intent to remake Final Fantasy VII as such. They've remade one part of it, but concluded it with an excuse for why they can't or won't remake the rest.