overstock question

Hi Guys,


I currently have a 2.5 gallon aquarium setup with a Betta, and 3 cCory
Cats. The Cory Cats average 3/4 of an inch. the Betta is about 2
inches. I have a Red Sea nano Mini Filter running on it currently.
Just yesterday I purchased an Aqua Clear mini/20 to run on this tank as
well. I am interested in maybe one or two more mid-level fish, like a
pair of guppies or neons? How overstocked do you think am I? I think
I will be fine once I get the AC running as well? The fish right now
are fine, they eat and do not stop moving around. I upgraded the
Nano's biological filtration with some AC sponges in various places
inside the Nano. I also plan to use them in the AC when it arrives.
Any suggestions to increase my biological filter? I would upgrade to a
5 gallon but I cannot fit a tank any wider than 6 inches where I have
it. This pales in comparison to my 120 gallon but...it is kinda cool
to have such a small tank. Thanks for any help you can offer.