Seeking input on early career decision

I have some career decisions to make in the fall, and I’m looking for any input anyone is willing to provide.

I have a summer analyst position coming up at a BB IBD. I am an ‘experienced hire’ (from a non-finance industry) and am late 20s/early 30s, so if it goes well, I think I’ll get an offer to start in the fall. I also have an acceptance to a top b-school (HBS/Wharton/Stanford/Booth/Columbia) with significant scholarship/finaid.

I honestly don’t know where I want to end up in 5-10 years, but I do know that whatever decision I make, I want to keep as many doors open as possible (staying sell-side, moving into buy-side, hedge funds, industry, etc.).

I’m going to do the summer position, but as I see it, I have three options after that:

1. Decline full-time analyst position, go b-school and shoot for post-MBA associate position. So in 5 years, I’d have an MBA and be a third-year associate, and my options would be (hopefully) promotion, or exit. My understanding from forums is that “exit” as a post-MBA associate is almost exclusively into industry, as buyside doors are not really very widely opened to associates who were career-changers. Is this true?

2. Accept analyst position and skip MBA. Not getting any younger, and I already have a quant-y masters, so considering bypassing MBA in favor of more years of experience in finance. Pros of this option are, as I understand it, better access (vs. an associate) to buy-side exit options in a few years if I don’t love sell-side. If I do love sell-side, I could hopefully move up to associate in around the same time it’d have taken me had I gone for MBA. In 5 years, I could still be close to promotion, could still move into industry, but would also have better access to buy-side options. My concerns w/ this course of action are a) no MBA would be a liability and b) buy-side recruiting targets analysts because of their less-specialized skillset AND age. i.e., is an older analyst as appealing as a 24 y/o analyst? Or is that a non-issue?

3. Defer b-school (assuming this is doable) for 1 year, get a year of analyst experience. This is risky in terms of rate of progression, since I’d still have to put in the same amount of time as an associate (right?) before having a shot at promotion, thus I’d be pushing a sell-side career progression back a year, basically. The plus side to this (and please correct if wrong) is access to buy-side options post-MBA would be on the table since I’d have that analyst experience on the resume.

I hope this doesn't sound careerist. I am looking forward to the summer and am definitely anxious to do a good job and learn a tremendous amount, and definitely not planning to jump ship from the firm who is taking a chance on me. But, I also want to make the smartest decision I can for the future, given that this is a career change and, thus, filled with uncertainties/unknowns.