If you really have an MBA from Harvard, I would be shocked to think you didn't already have a solid choice as to what career you wanted.
1# Sounds like a solid idea, but getting the connections to get the job may be tricky as far as the current job market goes.
2# Is near impossible. You'd have a lot better luck just working for a currently existing label. Starting your own label, and actually being successful are two different things, and they almost never follow each other.
3# Sounds like the most sensible choice here. If you've already interned there, you can tell them that, and put it on your resume. If they know you have experience in the field you want, and even better, experience with THEIR company, you already have a big leg up from a lot of other applicants for any job they have to offer. Plus, working for a big company like that offers opportunities for promotions and other great things.
4# Sounds the same as 3#, but if you were to choose between this and 3#, I wouldn't go for Sony. My advice is only in terms of actually getting the job. If you WANT to work at Sony over Viacom, I say go for it. But your internship with Viacom is a big leg up; one that you do not have in this case.
5# Only the slightest more possible than choice 2#, and yet, still dead near impossible.
Let's just clear the idea now that starting ANY company all by yourself, or even with the help of others, is a BIG risk. You'll spend a lot of time the first few years just desperately trying to make yourself a success, and a lot of what you initially earn will have to be paid back in the form of loans that you likely took to get there, or to help your company advance. Again, it's not impossible, just be prepared for a LOT of hard work ahead of you if you choose to start a company of your own. Also, if may do you some good to take a look at a website I know of that would help you with starting a business/company: http://www.bplans.com
In terms of pay, the only one of these that has a set payroll would be choice 1. 3 and 4 have set payrolls, but it would depend on the position that you would be applying for, which you didn't specify (be sure that the positions you want to apply for a re even available before you make your choices). 2 and 5 definitely do not have a set payroll, because having your own company means that the profit you make is all up to you. If you're successful, then you've made profit. If nobody wants so make a record deal with a no-name new business, then you've just lost a lot of money instead.