Would taking karate lessons improve my self-defense abilities?

Karate : Yes. Some styles are more suited to practical self-defense while other more traditional styles it takes time to develop the skill and expertise to be able to apply the techniques in practical self-defense settings.

Yes: karate will help to develop your strength and balance, and teach you good form so that you don't injure yourself doing a punch or kick. If you are ONLY interested in self defense, then a martial art that is more street oriented may be of more help. For instance, krav maga and Jeet kune do train wearing shoes and not in bare feet. It is only for self defense and not for tournaments.