Backtagging: It's all good, I'm willing to tag back as far as you'd like, but as things go forward we'll have to decide on details.
Threadjacking: Most of the time? Sure. Sometimes it gets complicated so if you're unsure, ask. Either way I can roll with it.
Offensive subjects: Nothing I can think of, but like before if you're iffy, ask me.
Preferred contact method: Plurk, IM and email.