I like to fully plant a new tank, start any fertilizing and/or CO2 I'm going to use, and let the plants start to grow for a couple of weeks or maybe 10 days. Then add just a small number of the fish I plan to keep, perhaps 3-5 fish only, and let them live in the tank for another week or more. Then add a few more fish that I plan to keep, so I have half to 2/3 of the total fish load I plan to use. Wait another week or so, and add the rest of the fish. That has worked well for me for many new tank set-ups. The numbers of fish depend, of course, on the tank size. I last did this with my 65 gallon tank, using 5 fish to start, and ending up with about 20-25 total fish.