Need Help Setting Up A Cory Tank...

[RJLB119]

This is no longer an emergency, but I don't know how to move this topic.  I would like to get feedback on the new tank.
 
I wrote out a long post, but I managed to refresh the screen and lost everything.  Here's a summary:
 
Tank: 20g Long
Filter: Aqueon 20 (has old tank's filter hanging on front just to help bacteria growing)
Heater: Marina 100W submersive
Light: Aqueon 17W T8 Full Spectrum fluorescent
3 live plants (2 ferns in rocks and 1 Egeria najas???)
 

 
Currently, 4 peppered corys.  I can't tell the difference between them.  1 has darker spots on whiter background, and 3 are very light spots on an opal/peach background.  The first picture is the darker cory with an opal one swimming through.  The second picture is of 2 opal corys swimming)
 


 
Ultimately, in many many months, I'd like to have:
6 peppered corys
6 tetras (neon or cardinal or ???)
2 otos
1 nerite snail
 
Does that sound good?  Will the filter be enough? 
 
Thanks!
 

 

[RJLB119]

My topic magically moved.  Thanks forum people!
 
I currently have 2 problems:
 
1) The marina heater is set at 75F, but the thermometers keep reading at 80F.  Do I just keep turning it down or is it a flawed heater?
 
2) If I have the Aqueon QuietFlow 20, is there a really small filter thing that I can add to that to help filter when I get more fish?  I don't really want to buy a new filter.  Plus the tank is completely covered (due to curious cats) so the filter would not have much room to squeeze.  Thanks!