Coco and peat have no nutrients, so I imagine that you should start feeding them as soon as roots appear.
If it's in nothing but water, then all the energy used for new growth is coming out of it's leaves.
(CORRECT ME IF I'M WRONG)
I've just started fooling around with coco.. so I may not know 'the best way' to start seeds in it.. but I soaked the coco with a dose of 240ppm (non-organic coco nutrients + kelp extract), after putting my germed seedlings in it. They seem to like it so far.
I've done the same for clones (with tiny tiny roots) that I put in coco.
For me, 1/4 of the recommended solution comes out to around 300ppm.
As for 'root repair'.. it sounds like something you'd use if your roots got damaged
If it stimulates root growth, then sure, give it a try. I would recommend adding this only to part of your grow, so you can notice any difference.
Your nutrients should have instructions on it.. recommending amounts for all stages of grow.. though sometimes you have to pick up the nutrient chart at the grow shop. Did you buy these online or something?