Ahh, the thought of keeping betta even if just one, in a larger tank with other communal fish. Such a nice thought.
Good luck btw, betta like people can just have a bad disposition. You would want to pick something that doesn't have anything frilly that would catch the betta's eye. Fancy guppies are a good example of what not to put with betta.
You really have to make sure your betta isn't stressed and stays well fed. Make sure you have a lot of plants in the tank so there are place for any of the fish to hide in incase they see fit. The betta shouldn't have really been in the presence of other male betta's before if possible. This makes them...hmmm...ornry? I guess that's the word.
Other than the fact that the betta might just attack anything that moves in the tank, any non-intimidating fish would do. Some people have had success with oto's, some with corey's (sp?). Some people put them in with mollies for some odd reason. Something that's very non-aggressive, and not too flashy, or with flowing fins.
The betta might go after a shrimp or vise versa depending on the size. Especially with a veil tail betta, they are very easy to catch on to, and tear their fins easily.
Just remember, lots of plants and hiding spots, well fed fish, perfect water.
The less stress, the less chance of the fish attacking one another.
Hmm, as far as an airator...hmm, an average pump will cost under $20 for a 10 gallon, a few bucks for an airstone. I'd suggest just spending the money on a decent filter. For a 10gal tank, you're looking at probably under $40. The most expensive part of the tank setups is usually the hood, for freshwater anyway.
Hope this helps.