From Mana DC here, Chocobo and Shinryu are one of our biggest worlds. as said above, the active times are 17:00 until 01:00 Japan Time so you wont have problems queueing if you play around those hours there are exceptions however like when it's tuesday reset, RF queues for Creator Savage would be active until 02:00 in the morning and dies down quick after that or when i270 anima step came out A1S queues were alive until 04:00. My datacentre might be a little more active for RF than the other two because it has Chocobo world in it (which is the NA Gilgamesh equivalent for raiding and all that) so if you're interested in the end game stuff you might want to consider heading to the aforementioned worlds.

Most if not all japanese i've met and interacted with are friendly and there's rarely trashtalk as long as you know how to play properly and/or do not hinder the party and even if you do make mistakes usually they're quiet about it unless it's serious play (RF Savage). OH and the one thing you might miss from NA worlds is that the cross world PF here is mostly business, no fluff .... unless the datacentre is crashing and you'll see PF entries screaming よしだああああああああああああ :P

other than that, Niqote and Serilda pretty much covered some of the other stuff you'd expect in JP worlds/DC