its not for learning from, its like a study aid, a revision guide if you will. you cant learn the pattern from them but you can revise a pattern that is rusty in your head. JMO
i agree with karatekid, if you have some knowledge of martial arts i think you may be able to get some knowledge outa it. you can learn some techniques and stuff. just have fun and go for it!
i very much doubt there is a weight restriction at dojos, everyone should be able to learn. and yeah im pretty sure you'll be able to get a gi in your size.