I think you are exaggerating a bit bro!
Nothing wrong would happen, nothing good will happen.
To be able to harm your livestock with ferts, you really have to overdose a lot.
If you go on vacations just lower the amount of light by raising the fixture and or shortening the time it's on and don't have them dose if you are using EI.
Plants are red because they are red, getting plants that are like that is key and a good amount of light. The rest is like talking about magic. I know what you mean by no nitrogen but its not just nor dosing nitrogen all the time, it's a "show" technique.
Note also plants store nutrients. so going on vacation they can survive with lower light levels EASILY with not extra nutrients added
for safety levels, do't be concerned
i've had 200 ppm of nitrates with no apparent fish stress, not that i try daily to do that, but my average is around 40-60 before water change, i feed my fish often, i dose fertilizers frequently, and my plants grow very rapidly. phosphates stay high as well. usually around 8-12 ppm
AND YES there is a difference between organic nitrates, and fertilized nitrates. organic( fishpoop) can do more harm tha fertilized nitrate, but again the tolerance is pretty high on healthy fish in a well maintained aquarium.
as pjerrey mentioned. red plants are red because the respond to strong light by pigmentation. they are protecting delicate tissue when they turn red. some plants don't need much to do this, some plants are more hardy and require much more light to do this. limiting nitrogen just allows less production of chlorophyll and the pigmentation already present to show through. it is not the key to a healthy plant