Visa sponsored jobs & Quant question

Hey,

yep, it's this time again - a high school student being worried about things he definitely shouldn't be; but it still bothers me a lot as I have no idea what it is going to be like.

So I am a student from Europe applying to HYPS and MIT, basically resolute to study Maths with CS (MIT offers double major, otherwise CS as minor); I am not completely sure yet what am I going to do after undergraduate studies, either Maths PhD, MBA or both. If I would decide to get a MBA, I would have to find a job for few years, however as a foreigner, I will need a h1b Visa sponsored job. I'd have to do that even as a PhD (maybe different kind of Visa), so the question is the same - how hard is to find such a job for a top-tier university graduate? Does having a PhD fancy my chances? I know that I could marry an US citizen, but a) I don't feel like getting married so soon, b) I would feel kinda ashamed, no matter how much I would love that woman...

My second question is a bit different. I am still unsure what can math graduates do in the industry (whether bachelors/masters or PhDs), but so far, a Quant analyst job looks like a match for me. In fact, I feel like it's a perfect match - I would work with math and CS, I would be proud of myself for having a PhD (you need that for quant, right?) and in the end, salaries are quite attractive. But there is a problem - is such a position going to be equally attractive as now in 10 years? Is it foolish to concentrate my whole education on one targeted job?

And lastly, a minor question: is getting both PhD and MBA a good idea? I am worried (geez, it's sounds retarded) that I might be stuck on a certain position with a PhD for the rest of my life. After reading around on the internet, I've got the idea that MBAs usually tend to end up as people who run things; they could start as analysts, but eventually work their way to leading positions. Is that correct or did I got the wrong picture?

Thanks.