너 너무 이쁘다 You're too beautiful (to be true). 너 너무 못 됐다 You're too nasty. 아주 means quite/so, it sounds a bit old-fashioned/formal to me. I use this one usually when I'm being sarcastic. I use 되게 more often. And we tend to use 너무 when we make a compliment. 진짜 sounds more informal than 정말(to me). 겁나게, 열나게 are slang. You'll hear young people(teens and in their 20s, 30s) say 겁나, 열라(열나) and other (eight? I'm not sure) swear words.

Those words are used as various meanings according to the situations. So you have to memorize the meanings one by one on each occasion. e.g. 그는 너무 뚱뚱하다 He is too fat. > 너무 too=아주=진짜=정말 그러나 나는 그가 너무 좋다 but I like him very much. > 너무 very much=아주=진짜=정말 너 진짜 그거 할거야? Will you really do it? > 진짜 really = 정말