Lease dynamics - MTM vs. long-term lease - are governed by the market more than anything else. 

If nothing else, it will add a lot of value to our own house if we improve the street a bit.

When I bought foreclosures, the bank wants at least their mortgage paid, else they sell at auction.

How else could you approach it?

If not in Boston, maybe somewhere else in the US?

Yes there will be some turn over costs, however, if we re-option it to someone else, we can likely get all of our turn over costs reimbursed through the new option fee of $3900.

I'm sure I've left out some details so please let me know else is missing from consideration!

If the neighbor maintains the grass, don't mess with it.

@Pierce Lovesee - while my accountant has assured me that an appropriate digital doc is an acceptable replacement for paper, I still keep paper copies of leases and scan everything else.  

If you're taking care of the aforementioned items and anything else that comes up, and all he has to do is put some money down, a 50/50 split is a great deal for him.