I've been thinking and planning in my head what my final stocking will be with my new 20 gallon tank. (LOL I'm kind of planning way far ahead, since I don't even have the tank yet).

But anyway, I came up with this set-up for a 20 gallon tank:

5 zebra danios
10 neon tetras
3-4 cory catfish
(for a total of 18-19 fish)

1) Would it be OK that neons would outnumber danios?
2) Would this combination cause me to be overstocked?

The combination sounds fine, there may be too many fish though and it might overstock you. I'm not too great on stocking rules, but maybe less neon tetras to lessen the load a bit. It would be fine for there to be more tetras, I'm just worried about the stocking is all. I hope this helps!

I think you could get away with it if you had adequent filtration. What kind of filter you gonna run?

sounds like a active tank, I think it will look nice.

Keep up on your water changes. Water changes and good filteration is key.

Well, I'm not sure exactly what filter, but it would be the one that came with the Tetra 20 gallon kit...... Probably one of the whisper brand ones.

Maybe a few less tetras, 8 sounds like a good number.

You need about twice that filtration to suppost them fish. For a 20g I would run a 40g rated filter.

I have about 15 tetras (3 different species) and 4 cories in a 20 gallon and things are fine. I run a biowheel filter that, as mentioned, is made for a larger tank, and I do a weekly water change (about 20%).

I also have the tank heavily planted which helps give the fish places to get some 'personal space' from one another and keep the nitrates in check. Have you thought about planting?

I've thought about having live plants, but for the moment I'm concentrating on actually getting the tank, cycling, and getting all the fish situated. For right now, I'll only have fake plants. Maybe in the future....

Live plants are not really any harder to care for. As a matter of fact, they are easier than fake as they keep the algae on a down low meaning less labor cleaning the front and they aid in filtration. I would definatly atleast consider Anacharis in there floating.

Most live plants aren't hard to care for, at least the plants sold in pet stores. They all tend to be swords, anacharis, or water wisteria. I would say start with fake and maybe add one plant later on to see if you like them.

Yeah, Sushi, that sounds like a good plan.

I don't really know anything about keeping live plants, do you have to have fertilizer? Can you just cover the roots with the tank gravel?

Covering with gravel is fine. You can use fert. and it is better to do so but not required.