You can get really creative with healthy snacking - there are some things which are considered 'free food' on JC which my partner and I snack on.
For example - fat-free salsa (for chips) is pretty low-cal and a lot of the stuff they use in it would be considered free food. Whack that in some tupperware with some carrot sticks and you've got a fairly portable low-cal snack.
Tomato slices on lite crisp-bread with some sea salt is yummo. We also put on 'Sambal Badjak' an Indian chilli chutney type thing. It's so hot we can't put enough on anything to count its calories.
For general food bulking out we make an awesome bake of slices of eggplant, zucchini, mushroom, onion, garlic, turnip with each layer drenched in a tomato-based pasta sauce.
I'd avoid ANYTHING with high-fructose corn-syrup. We have far too much sugar in our diets - what with all the breads, pastas and junk food we eat. That sort of thing will slow down your metabolism so fast it'll make your head turn.
Check out some of the low-cal recipe books. The pictures make it easier than online searches.
As to the lifestyle stuff:
At Uni I studied Opera at the Queensland Conservatorium. At the time it was the best vocal institute in the country. It was great and horrible at the same time. I was the only one in my class to graduate and the entire process destroyed my love of music and performance for many years to come. After a few years I got back into it, formed a band and gigged around Sydney. Enjoyable as it was, it was never the same and even today music is something I'm a little conflicted over.
If you found the right institute that both pushed you hard AND encouraged you then the music angle could work out. Just bear in mind that there's *very* little call for classically trained musicians in any kind of venue that's likely to make you anything like a living wage. Doing it for the love gets old when you can't afford bread. You have to be better than every single one of your peers to be able to get the choice positions that provide enough for you to live on.
Otherwise you're stuck teaching music, either in school or privately and doing the odd show for your local community theatre. Either way, it's usually not enough to satisfy the passion that brought you to music in the first place.
I'm not trying to discourage you - just bear in mind that if you want it, you have to *really* want it. More than anything, more than breathing. And you have to be willing to give up anything, do anything and focus entirely on it as a goal. Only then can you hope to compete at the level that it's worthwhile.
As to design. I really love it. I spent nearly eight years developing and teaching multimedia, design and film courses in addition to doing most of the marketing for the multi-million-a-year college. Had about a $250K a year budget for my marketing & design.
These days I'm a freelancer. I work from home most days. Get up late, go riding around Melbourne's parks on my bike and come home to my office where I work with my wife in a big-ish loungeroom overlooking the water in Melbourne's docklands. It's great. I also work with a programmer to develop new web applications (similar to traineo, but for other industries) that make more regular income than just one-off design work.
I had an odd route to getting to where I am and for most people the first years of being a junior designer can be pretty lean, cash-wise. If you can get together a kick-ass portfolio, get a position as a junior in a cool firm or two and do that for a couple of years you can then go freelance, make great money, keep your own hours and choose the jobs you work on.
Overall, it's pretty cool.
My Dad was a maths major, in the top 1% of the country. He wound up a teacher too.

Again, not a lot of call for maths unless you're super good, super motivated and want to work in some very esoteric areas.
No doctors in the family, but my doctor friends have done well in life. Bear in mind they're in their mid-30's, still studying hard for their specialties (the way to make great money in medicine) but they own their own houses and lead a great life. They can have some pretty antisocial hours tho!
If there's any more questions, feel free to ask.