First of all, welcome to the shooting community! I'd recommend starting off with USPSA pistol matches for an intro. Not as complicated as IDPA and not as gear intensive as 3 gun. Try before you buy, too. Borrow and/or try other people's gear. Ask questions. Observe what others are using. Your own gear selection is limited only by personal preference, budget, seeing what works for most shooters, budget, your own goals, and budget.
If I was just starting off in 3-gun, I'd get a Glock 34 with some decent sights (front sight with a thin blade and a fiber optic), a Stoeger M3K with a mag tube extension (10+1 total capacity), and an off-the-shelf-ready-to-go-for-3-gun AR. Safariland ELS/QLS belt system with their mag pouches and a pant load of ammo (no steel core rifle ammo, please). Most important and effective investment is training from any of the 3-gun gurus. That alone would put you ahead of the starting block.