Agree there that in the remake, everything was better than in the original in terms of characters, world and introduction to the lore of the game as a whole.
Negatives were the padding (which I didn't mind it so much as I ended up liking the combat, which is also fairly advanced in terms of easy to learn hard to master), some graphical glitches and the fact that it wasn't the entire game. As I said back in my "review", once this is compete, if they keep up the quality of the fist, it could be a 10/10 for me overall.
In terms of progress of the next part of the game, I guess it will depend on if it is stand alone or lets you progress right where you left off. Max is 50 if you grind/do hard mode. If not you'll be between 30-40 at the end (I was 38). They could theoretically do it quite easily.
You exit into the open world where you soon encounter Yufie, which steals your materia. They change exp gains to where level 50+ increases quite a bit, so people who didn't grind will level up quickly at encounters at that part. By the end of the Yufie section, people who did hard/grind only would have a 1-3 level difference compared to people who didn't. They could easily make it so level 50-51 = exp required for 30-40. You might have a few maxed materias, but that could easily be dealt with by having "Fire 2" and such, so you upgrade. So you'd gain some bonuses by having played the first part for longer, but not required.
They might not do stand alone parts, but rather you buy "part 2" and it just adds the chapters to the game you already own (hence no "part 1" in the title of this game).
Plus side, they could deliver more content to the game quicker (which the developers have said they want to do), downside is that it would also enable a possibly predatory purchasing model. I also don't like other gaming companies getting the idea that it is ok to split up a game like this, because it really isn't.