Sotenbori is already known to be in the game. Only thing not known is the map they are using - Kiwami 2's or 5's... But the battle dungeon/arena stuff is in there, basically long, optional dungeon battles with strong enemies. Can't wait to dig into that.
Price wise I think I got my copy for technically £50. Well, the HKD $500 card was that much, but I basically have almost 100 of that left over, so that's getting spent on DLC for the game when its released.
As for trophies. No. 3 is not easier. 4 is the easiest, then 5, then 3.
4 has no 100% requirement, and most mini game requirements are easy. Even Mahjong has an easier hand to get.
5 isn't hard, just really long. With enough time you'll get it.
3 though. Mini game master alone makes it harder - EX Hard batting cages, expert pool, naked hand in Mahjong... There's less content in 3 compared to the other games, but its 100% completion clear for mini games requires way more skill.