Pehag

Because they were working together for a much longer time to make the idea of an alliance easily accepted they would have had plenty of time to work on all the specifics and things they wanted while doing that.

If it's anything that happened in this chapter it's all cannon.

I guess he would be a cross dresser?

Regenerating entire limbs was never easy in DxD reattaching them was with Phoenix Tears but since he teleported without his arm he wouldn't be able to get it to reattach.

If you've ever watched or read Seraph of the End you'd understand a bit better but basically they are vampires that have turned into a being that lives off the desires of others. I'd recommend looking into a bit more if you're interested since there is more than what I just said.

posted in the last chapter

I guess I didn't word it correctly. Rizevim created a separate space where he couldn't just leave if he wanted too so he didn't really have a choice in fighting Rizevim. Sure he didn't have to enter but like he said he didn't know it was Rizevim and thought it was some random weakling not one of the strongest beings in the world.

It's more on the level of it would take to much time. If they fought for a couple of days or so he would end up winning sure but during that time Ashera could just run away instead of fighting. Besides since they're on the same level Sirzechs wouldn't get out of the fight scot free even if he did end up killing Ashera so it's just not worth it.