For recoil of pistols check out this YouTube video
https://www.youtube.com/watch?v=WzHG-ibZaKM, for the most part shooting two pistols at once is a HollyWood thing, as all you really do is miss a lot with one of them. The human eye can only focus on one thing at a time. If you are shooting both at the same target you will do much better than if you are doing the holloywood thing of one gun each hand and each pointing to one side.
As for the body armor it is kind of hard to say, yes more is better but it does not always make a difference. For example if you have a level IIIA vest and you put a second level IIIA vest that does not make it a level III vest. If you are wearing the two level IIIA vests and are shot by just about any rifle it will go through them like they were not there.