Use your best judgment on who you decide to ask - there is no set formula for who should be your recommenders. We know it is not always possible to have a direct supervisor write your recommendation – we would not want you to jeopardize your current position for the application process. Look at the questions we are asking recommenders to complete. Find people who know you well enough to answer them. This can be a former supervisor, a colleague, someone you collaborate on an activity outside of work. How well a person knows you should take priority over level of seniority or HBS alumni status.
I don’t think it will sound unrealistic as long as you have a demonstrated interest in whatever you’re pitching… generally to make a non-business to business move you want to tell a story such as: “I was interested in Topic X, but then I ran into Person Y / Went to Event Z, which sparked my interest in the business side of Topic X. Now I want to combine my knowledge of the field with business and eventually… become an investor / advise companies / start a company / work in sales or business development in the field.” The list goes on since business schools offer such road topics.
There is no 'except for maybe "x"' on your list. With a 690 you could get dinged at all or accepted at all. And the same is true with a 760. I have a 710 and got in everywhere I applied (including Texas, Darden, Ross, and Fuqua). I am a white male with 4 years of financial svcs experience (non-bb s&t), a liberal arts degree from a regional private school, dropped out of a previous grad program with a (stopped going to class)..my undergrad grades were good but that's pretty much it. No community service, no leadership bs...just good recs and good essays. I know a guy with a similar profile but with better grades, better work exp, and a 770 and he got dinged at Texas, HBS, Wharton (no interview), Booth, and WL'd at Darden. I repeat, the GMAT is merely what gets you looked at, and that bar is far lower than you imagine. Many of the others responding on here sound like 20 year olds with no clue as to the reality of mba admissions. That's ok, I didn't either until I went through it. Apply wherever you want, just have a good reason for doing so.