Number one tip is a bigger tank. It'll be easier to keep clean/water changes, and he'll be less likely to get opportunistic infections like Ich.
You can usually find the plain glass aquariums (sometimes called terrariums) for close to a dollar a gallon (10 gals are usually 12-13 dollars), even when not on sale. You can get them at Petco, Petsmart, and often even WalMart. They don't come with a lid, but you can use the OFL method of plastic wrap secured over the top of the tank in place of the hood. I do all my tanks that way, and it works really well, just make sure you leave a section uncovered for *some* air movement.
With the bigger tank, you can cycle, which will make your fish much healthier, and your life easier. :)
As for cycling...on this forum most people will tell you not to use "cycle in a bottle" products, some because of not using chemicals, others because they say they don't work, still others because they say that it's impossible for the bacteria to live in the bottle. Other forums have people who say that certain brands are great. I know a lot of them *do not work*. But, I've got five tanks, divided in various ways (3 20 gals and a 30 gal) and I've used the API Quick Start, and it's done a great job. It's been several months, and my cycles have all been stable, and I test frequently.
Prime also makes a cycle starting product, but I haven't tried it.
One note about the bacteria in a bottle, once it's opened, you need to use it ASAP, like, within 48 hours, otherwise the bacteria dies and you're not actually adding anything useful to your tank.
When you do the cycle in a bottle, let your tank set up for a week or so, or until you get a 0.25 ammonia reading (when you'd normally do a water change) and *THEN* add the cycle in a bottle. This gives the bacteria something to live off of, and within 24 hours my readings have all been good. Ammonia should be at 0, your nitrite should be low but with some reading, and your nitrates should be going up. Within a week, your ammonia and nitrites will be 0, and your nitrate will be 40+.
I hope that helps!! :)