OOOOooooooof... This is a Novel!! And a bit above my head on the technical aspects of it. As far as the injectors go, sourcing, I had to replace 2 of them on my VG30 not tooooo long ago. Maybe it's been a couple of years now... maybe... I replaced them with the Beck-Arnley version of them. Found them on Rock Auto. I don't recall how many they had, but I only got the 2 that I needed at the time.
I looked not too long ago to get the remaining 4 done, but finding NEW was becoming unobtainium. I wound up getting 2 Standard Motor, and 2 Rebuilt ones that I haven't found the need to install yet. The 2 good "New" brands that I would stick with are Standard Motor Products and Beck-Arnley. Beck usually re-boxes OE stuff, or that's what they did in the past. For imports, they're pretty solid. Standard is usually pretty solid as well. If you punch the part numbers into Amazon, you might be able to find them there as well and not get gigged for shipping like Rock Auto. I would always buy new if you can avoid the rebuilt ones. I have no real experience with rebuilt ones aside from 2 that I got off of Rock that have not been installed. With the age of these, you get what you can get I suppose.
BTW, the 2 injectors that I replaced made a world of difference in the idle and perceived power. I have some steep hills that I don't lose power on anymore that I used to before the swap. Upgrading the injectors might not be a bad idea, but if the rest of the engine is stock, you're probably better off keeping it stock.... but don't go the cheapest route. That doesn't always work out in your favor.