Weeeeelllllllllll.....this is coming from an old timer, my IDPA # is A0762.....been shooting since it was first organized.
IDPA was started as a way for people to shoot what they actually carried, not necessarily to have to get a gun just for competition.
It was started by Larry Vickers, Ken Hackathorn, and Bill Wilson (and I know I'm forgetting a couple people, forgive me) as an alternative to IPSC, which had totally gone the way of the game, away from the roots that Col. Jeff Cooper and Ross Seifried and others started IPSC for.
Street guns with street holsters, in (relatively) more realistic scenarios.
I've used M1911's, Beretta 92's, CZ-75's, Glock's, SIG P226's, HK P7M8's and P9S's, S&W 19's, M&P's.
Ultimately, I'd suggest getting into it with what you have and then seeing where you want to go.