well, im no expert, as i have just done my second ever spawn, but i can tell you what i have learnt and what i plan to do so that you have an idea till someone more experienced posts :D
I believe it is okay to start topping up the tank a week after the fry have hatched, although if your water parameters arent looking too good then it is best to start sooner.
I am planning to top up my levels very slowly, like an inch at a time. I also intend to base it on how many fry there are. I want it to be easy for them to find food, and the less water they find it in the better, but you also need growing room. its about finding that balance.
Once I am happy with the... fish to water ratio i suppose, i will be doing 30% water changes daily. the more water changes, the faster the growth of the fry. it is best to get as much of the dirt off of the bottom as possible, as this is what will polute your water and maybe even cause your fry to not develop properly.
as they get bigger, i will move to my bigger grow out as they wont be struggling to find food. Once they are in here, I will do water changes every other day, 40-50%
I am only going to be using IAL and a normal dechlorinator, probably my equivalent to aquasafe.
Hope that helps get an idea of how you want to grow out your spawn :) you can do less water changes than this if you are tight for time, the only annoyance is that they grow slower. So long as you keep testing the water, you will be fine. good luck with your spawning!