Or maybe they just realized that if they brought in the big hero on the good side from the start, it was difficult to have sufficient growth for Rey and Finn - regardless of audience interest.

The next movie, in my view, will be less bound by the old fans' expectations than TFA - and people may be overestimating how much TFA was, to begin with. One way or another, Luke will have to mentor Rey and then get out of the way - killing him off in the finale is one option, albeit perhaps a bit unoriginal.

I don't think the makers/writers are nearly as nostalgic about the characters as the older generations of fans, and both the massive box office success of this movie and Disney's general focus will be pushing them towards the newer viewers - in whose view Han Solo wasn't all that important, nor will Luke be unless the plot requires him to be.

Sort of agree, although if he is indeed 'broken', it's another case of what I said about Kylo Ren in my previous post - not easy to get an audience to buy in to all that backstory if you can't take the time to really show it. And somehow Star Wars doesn't seem like the series to go with extended flashbacks? Old Jedi sites or some other kind of ancient history seems likely - after all, the Force has just 'awakened' again. Which no doubt would be linked one way or another to Snoke and the power sources of the First Order. As I mentioned, I'm probably more familiar with KotOR than with any movies, so I can't help being reminded of the Revan plotline.

Could go either way, depending on how important Luke remains. If they indeed limit his role, or indeed kill him off during the second movie, it can be earlier.

Yeah, I'm not so sure about that, as mentioned above. The emotional side of things, anyway - viewed from a simple plot perspective, you obviously still have the usual mentor problem of nearly every fantasy story. Even if Rey does seem to have remarkably little need for a mentor.