Re. personal defense: wear shoes you can run in if you lose the bike. That's it. Any threat is likely to be bigger than you, probably from two or more people, who may well have knives even if you haven't seen them. The person who suggest "martial arts training" is just being silly - most martial arts don't prepare you for a street fight, certainly not against multiple and possibly armed attackers. Maybe if you boxed and did MMA for a couple of years, had exceptional talent, did a lot of kettlebells training, and lucked out on the knife thing.

Re. tyres: Marathon Supremes have excellent anti-flat protection and speed, and maybe you could anti puncture gunk.