Hi marcie, I'm so glad you're excited about fish keeping. It's a great hobby and it's easy to become attached to your fish.
Your tank is 5 days old? Do you have a
test kit? I see you don't know about the
nitrogen cycle, here's a basic explanation of it:
First your
ammonia (from fish waste and left over food) will rise.
In a few weeks you'll see the
nitrite levels rise and the ammonia levels start to drop.
After a few more weeks you'll see the
nitrate levels rise and the nitrite levels drop.
Ammonia and nitrites are toxic to your fish.
So until your cycle is complete, you need to keep the levels down with daily water changes
When you having readings of 0 on both ammonia and nitrites with some nitrates showing, your cycle is done.
This link will explain more about it:
http://www.fishlore.com/NitrogenCycle.htm
Prime is a good water conditioner to use when cycling with fish. It detoxifies the ammonia for 24hrs between water changes while still making it available for the beneficial bacteria.
Since you've been forewarned about the betta being in a community tank. The only thing I will say is please have an alternative plan. Things can go bad quickly. It's not only the bettas temperament you should be concerned with, it's the other fish going after the betta.
This is especially since your tank is overstocked.
Good luck and post some pics soon.