@Wintry93 To be honest it may be a bit as I want to develop the world of DxD and the characters properly. Even then though I don't intend on delaying the timeline longer than strictly necessary.
Once this "original" arc is over, there would be maybe a handful of chapters concerning the likes of Sairarorg, Kiba, and the like before jumping into ep 1 proper.
Sorry if its disappointing to hear, I simply wish to develop things properly. This is likely going to be a long-ish story due to that wish.
So as an example, things like training Issei or spoiling Asia because she's adorable will also be in the story to develop everyone well.