First of all, a couple of definitions.
Shoaling fish are those species that in the wild live in groups of hundreds, if not thousands.
Schooling fish are those shoaling fish that always swim together in a group.
Non-schooling, shoaling fish do not stick together in a group in the tank unless they are stressed or afraid.
Shoaling fish, both schooling and non-schooling, need to be kept in groups of the same species. If there aren't enough of them, they become stressed by the lack of numbers. It is usually reckoned that they lose count around six, which is why that is the minimum number you should have in a shoal. Though some people reckon they can count higher than six, and the shoal should be bigger.
Fish of similar species will stick together when forced to by lack of their own species, eg your zebra and pearl danios, but they are much happier in groups of their own species - even if they do not school and all go their separate ways in a tank, they know there are others nearby to school with if something threatens.
When doing a fishless cycle dosing to 3 to 4 ppm ammonia, you should be able to get about two thirds of your final socking list as soon as the cycle has finished. The fish to leave till later will include species that need a mature tank (one that has been running trouble free for 6 months).
Using the community creator (I have assumed your tank is 80cm long because that's what mine is
) you are currently 22% stocked. Increasing the four species to six each pushes you up to 45%.
You have room for some bottom dwellers eg one of the dwarf species of corydoras (pygmaeus, habrosus and hastatus, though only habrosus are in the fish profiles on here) and perhaps a centrepiece fish.
Whichever fish you decide on there are a couple of points to note.
You need to get them within a few days or the bacteria you spent a while growing will start to die off as you don't have enough fish at the moment to provide enough ammonia.
The danios like the temperature a bit cooler than most tropical fish. I would look at fish that can live happily at 23 to 24 deg C, and set your heater for that temp.
Do you know if you have hard or soft water? That info should be somewhere on your water company's website. Fish will be healthier if you choose those that prefer your hardness - hardness is more important than pH.
One other thing - for testing pH, run a glass of water and test it straight away. Then leave it to stand for 24 hours and test again. You'll probably find they are different. The pH after standing is the one to work with.