Is everything well? Im a beginner!

Question
I am relatively new to tropical fish keeping although my family have fish tanks. I keep freshwater fish - a lush mixture of colourful very small guppies and one molly. and  a male simese fighting fish, some tetras (neon). They are all doing very well. The water has matured and so on,
More details below:-
Air pump,
Testra heater,(set to 25 degrees)
Thermometor (excuse spelling)
sand/gravel (fine, black)
1 rock for hiding, (small)
1 large pebble
1 real plant
3 way filteration system mecanical, chemical and biological, (utilising sponge, ctivated carbons and bio balls which i changed twice  4 weeks in).  

feed small quantities of fish 3 times a day, fluoresent light on 10hrs a day, and shrip food for a treat.

I use Testra 5-1 testing kit, to do regular readings,
I use Safewater, (conditioning liquid) for every water change, which I frequently do (daily 10%)
I clean the gravel every 3 days,
I use Filter aid, and sometimes bateria killer (liquid sorry do not know exact name without grabbing the box!)
and oxygen tablets every other day.

I have a 5.7 US 21.6 Litre tank i believe, hexagon.

The question is, they all seem very happy and very content, they are sparky, vibrant and alert. The guppies are as frisky I take it this is natural!

I wanted to only keep small fish - no more than 3cm each because of my small tank.
Here is what I have
guppies, one molly and one (the biggest fish in the tank) Chinese fighter (male).
All seem happy, and I was just wondering if everything seems well. I am enthusiastic about this new hobby, but more importantly wish my fish to keep happy and not over crowded. I have in total 11 fishes the smallest being 3 of them at 1 little cm.  

How much more, or how less of fish - need all the best advice I can get.

Many Thanks
Sara :)

Answer
Sara-
Welcome to the fish keeping hobby!  It is wonderful that your tank is up and running.  While right now, the tank may be active and well, as the fish get larger, they will outgrow the tank they're in.  The molly will get much bigger over time.  I'd recommend eventually moving up to a 10 gallon tank for this number of fish, but for now, they'll be just fine.  You're diligence with the water changes is excellent, and in the immediate future, you'll be more than happy with your setup.  Enjoy!