no worries dude!!

In my 25g skimmerless but heavily planted tank, I have a yellowhead jawfish, black leopard wrasse, 3 yellow clown gobies and a Cassiopeia jellyfish. Shutting down tank as part of my summer reorganization project, but the fish are all healthy and the macro does a good job sucking up nutrients. I use C. prolifera for nutrient export.

There is no exact number of fish you can have. There are so many variables, plus you will want to add fish slow anyway. Avoid tang as they need more room to swim, go with smaller species. As you adding more fishes to your tank, watch for your nitrate level and how your current fishes are doing. If nitrate level is low and fishes are happy, then great you can add another one. If you nitrate is high and fishes are not happy then you know you are adding too much with your current system. Time for upgrade :-)