Lots of questions but I think I can answer all them in one response. In choosing any martial art, you want to find one that best serves your purpose and fits your body type and personality. As an example of what I mean by body type, if you are big and powerful, then a soft, graceful style would probably not be a good choice for you. As an example of what I mean by personality, it you are a quiet, non-aggressive person, then full-contact fighting would probably not be a good choice for you.
As to your purpose, you state that you are looking for a martial art that concentrates on self-defense. All types of Taekwondo are sports oriented, and most traditional styles of karate concentrate on the budo, the way of life of the martial arts. These arts may be used for self-defense, but that is not their primary purpose. Some people think kickboxing is good for self-defense, because it uses full-contact, but it is still a sport and uses safety rules and equipment. One could still argue that, on the street, it is better than Taekwondo, but self-defense oriented martial arts would argue that it is a poor replacement. The same arguments may be made for the mixed martial arts. All these arts train against likeminded opponents; whereas, in self-defense situations, you will most likely be defending against people who untrained in any martial art, they are just evil, mean people who will risk their own lives just to hurt you.
If you only want to be highly effective at self-defense, then you should choose a self-defense oriented martial art, such a Krav Maga. However, a problem with these types of martial arts is that you do not get the enjoyment of physical competition against other people that you get in other martial arts. If is near impossible to find a martial art that has competitive sparring and also is self-defense oriented.