I picked this up in Japan last month so can answer a few questions:
1. Its super easy to miss the 3rd term (Jan-March). I ploughed over the game and ended up getting the normal P5 ending.
2. You do get extra stuff & money if you have a save file for P5. You can choose if you want to enable the extra stuff when you start a new game in P5R. I should add I have completed the Japanese version of P5 so no idea if it took the PAL or JPN save file.
3. Any new game + benefits from P5 do not get carried over to P5R.
4. Just like P5, starting a new game + on your 2nd game of P5R does get carried over plus extra stuff too. I took a photo of the new game plus screen so I can find out exactly what.
5. If you stealth an shadow with a surprise attack you get a different battle song.
6. The deeper you go into mementos the more the music changes.
7. You can't reaper farm
or at least after trying for 4 hours I couldn't do it on a flu day.
If you have any more questions let me know, I'll answer them!