It really is up to you. Mech is good, it's got more math than chem. But don't think that chem is totally math free. Engineering is about creating things. You'll be a little underpaid for your efforts, and the best engineers are the ones who are in it to invent and create.. so just pick whichever suits your interests the most.
Do your Bachelors degree first, then decide whether or not you want to (or even can) do your Masters. Engineering is a very powerful core, because it really trains your mathematical skills; I know dozens of people with a Bachelor's in Engineering going to all sorts of other fields, including business and finance. It shouldn't be tough to move from Mech to Aeronautical.. I myself moved from pure Electrical to Telecommunications/Signal Processing.
Personally, I went ivy league, had a much tougher time in class than many, but after all the pain, I got quite a good job. I'd say I enjoy my job, very flexible hours, excellent chances of promotion, and I'm more irreplacable than some people in management or sales.
It depends.. some people graduate, get cool jobs, big houses, have their own patents.. and some design those toy cars that break down after a while. Many companies see engineers as the people who "use up money" and sales as the people who "earn money", and your wages will be a little biased towards administration's love for you.