1) boarding is typically through the door between Y-J
2) have you check how much $ for E+? Personally, those Airbus 330 are great on the 2 side part, or if you find an empty middle section. I've done my share of international flights in Y on these birds way before they had E+ and loved them. At the moment, AA upgrades Y-J. Nothing official has been mentioned regarding Y-E+ upgrades using SWU.
3) cant comment since if not flown them with E+, but I presume the front seats might be the least desirable due to its proximity to galley. I prefer the back rows.

This is still considered a 2 class plane.