You should carry what YOU can shoot well and will carry the most. As to size and what thugs think...who cares? If they want to be stupid and find out how deadly any well placed pistol shot can be at close range by attacking you, feel free to oblige them.
As to spare mags - I'm a rare breed of OCer. I ditched the mags and replaced them with back up guns. Why? Much easier/fast for me to go to another pistol then fumble for mags under stress, then reload. In a gun fight time is NOT your friend. Shave off every split second of time you can when possible.
If you do carry a spare mag(s) in a pouch, practice (safely) drawing them & loading them until it be comes as fluid as possible.
I am not answering your question directly because - what works for me, may not work for you & like wise. Experiment (safely) and find a pal that can go over (faux) stress /force on force drills with you such as pistol retention, and playing the moving/shooting back bad guy while you attempt to reload (USE Snap caps or AIR SOFT) etc. It may sound goofy, but air-soft can really help you develop real world skills, while maintaining a safe environment. If you go the AIR SOFT route wear protection - they can: knock out teeth, eyes etc..