Need some camera advice

[canonfodder]

19. Either camera is fine

Sorry this is a bit late.
Just now noticed your thread.
Either the T3 or D3100 will suit your needs. Both are pretty much equal in capabilities.
Physical sensor size is nearly identical. The sweet spot for the aps-c/DX type sensor is right around 14mp.
The D5100 is about a hundered bucks more.
If you opt for the T3, I might suggest you make sure it comes with the MkII version of the 18-55.
I know Adorama has the T3 plus the MkII 18-55, 55-250mm bundle for $650. Not a bad buy.
For your needs, I don't think you really have to go much more.
If you find you really begin to enjoy photography, you can always move up at a later date.

A couple things you might keep in mind when shooting indoors without a flash.
Run your iso up to at least 1600. Higher if you don't mind a bit more noise creeping in.
Set the white point for the type of light.
Do not use aperature priority unless you use a tripod.
Use shutter priority, and go 1/30th of a second. Faster if light permits.