Yes, there are betta shows, but there aren't that many. The first one in my state happened not that long ago, and I have to wait a year to go to the next one :P
Because bloodworms and brine shrimp are treats, and betta fish are really tiny, I wouldn't advise giving more than one or two a day.
Two bettas can share a divided tank. Here's a good link on how to make an inexpensive tank divider: http://www.bettafish.com/showthread.php?t=40025
While you could make it work and divide the five gallon in half, many people will say that five gallons is the minimum for one betta fish. If you want to divide the tank into 2.5 gallons per betta fish, any other fish in the tank would have to find a different tank to live in.