when do the fish get added and how many
It's Day 14 since the tank was set up, and besides the fish that were in there to start the system cycling, I don't think that it is ready for fish to be added yet.
Some of the plants have grown a little, others have died back. However, it does look like it is establishing well. We have added 10ml of Seachem Excel and 5ml of Seachem Stability a day. I also changed 20% of the water on Day 10. The fish in the tank have been fed a tiny bit every day - still keeping them hungry and being sure that there is absolutely no chance of left-over food discomposing. As a rule, it is far better to under-feed a tank than to over-feed it.
There are a few "rules of thumb" as to how many fish a tank can accommodate. One of them is "an inch of fish for a gallon of water". However, I feel that that over-stocks a tank especially if you have large-bodied fish like Discus or large Cichlids. There are fish that generate a lot of pollutants like goldfish, and while an inch of goldfish for a gallon of water might work, you need 2 to 3 times the amount of filtration. You also have to remember that the fish will grow and might out-grow the tank. Also, if the tank is odd-shaped like my very deep tank, the inch per gallon formula would not work. You will also have to factor in the space taken up by gravel and rocks and reduce the volume of water accordingly.
Another "rule of thumb" is 12 sq.inches of surface area per inch of fish. Again, if you have very active fish like a school of Bala Sharks, that may be insufficient. With my tank being 60" x 18", using the second rule would allow me 90 inches of fish. Using the first rule, I would be able to put in 140 inches of fish. It would always be far better to understock the tank than to overstock it.
As to how much fish to add at any time, a rule I use is not to add more than 25% more fish at one time. So, for example if I am going to stock my tank with 60 inches of fish (eventually), I would add no more than 15 inches of fish at a time. Allow the tank to stabilize as the biological system will need to catch up before putting in more fish.