The thing you want to remember about both Aikido and Tai-chi is that they're extremely complex. They are highly effective and powerful, but you have to put in a lot of time and effort in training in order to reach that level of effectiveness.
I don't think you would have to worry about fighting thugs who know kungfu. Thugs don't last long in a school or dojo, which requires great dedication and patience, two important values that thugs tend to lack. Most trained martial artists don't pick fights, they end them. You most likely will never face off against a martial artists, as you're more likely to sit down and and drink with them.
Aikido offers so much more than just a fighting system, it's also a way of life. You will learn how to deal with folks even outside of combat situations, and how you should act so that you do not provoke any violent reactions from others.
In response to your combination punch worries, the thing about those is that they're basically punches that flows down the centre line. If you learn Aikido well, you'll know to get off the centre line immediately, and then either evade and escape, or apply a technique of some kind. Hook punches that flows from the outside is slower, and as a result, it isn't usually included in those rapid combinations. Never try to block all those punches, a master may be able to, but you wouldn't be able to do that until after several decades of training. Get off the centre line, that's how you avoid getting punched.
The only thing you can do to see if Aikido is for you is to try it. Most dojos will allow you to try out for a class or two to see how well it fits you.