This is my second batch, I have 5 plants and i will do one diary for every plants.
Also for the first week i'll use a tent 80*80*160 cm and then i will move in a 100*100*200cm tent.
For the Elycitor i put 0.3 mg in 1L of water, once by week, and i don't mix with the others nutrients.
This is exactly the time when you want to do that - actually, the third week of flowering is when you generally want to start that sort of thing - so since you're in the 4th week, go for it! The grow is looking great!
Good luck!