Sven has given you an excellent answer to both parts of your question. I agree that different ways of saying the sentence about professional experience are simply an issue of formality. 'Haven't got' is more informal than 'Don't have', and 'a lot of' is more informal than 'much'. So, if you want to make the distinction between casual and formal use, I'd swap the expressions round: 'I haven't got a lot of professional experience' = informal/spoken 'I don't have much professional experience' = slightly more formal/written

"I'm a kind and cheerful person" is probably the best one, because it rolls off the tongue most easily. The other two can be used provided you use a comma between the two adjectives. "I haven't got much professional experience" and "I don't have a lot of professional experience" are both right and mean the same thing. I would say the former is a bit more suited to written language and the latter is a bit more suited for spoken language. But they can both be used in either situation.