I would also say go with your 1911 if that's the one you shoot best. I know that's the reason I use mine for IDPA.
Read through the rule book on the IDPA website to get an overview of the rules and what gear you're aloud to use but all the info you've already been given is good advice.
It did get me shooting a lot more so I switched to shooting 9mm to keep the cost down, it might be something worth thinking about.
Most importantly, take your time and have fun.
And Happy Thanksgiving.