You might want to look at the leasehackr site and/or the edmunds.com i3 forum -- I've posted details and analysis of a deal I recently did in RI as well as helping others figure out their offers.
For a lease, you need to negotiate the 'purchase' price, and also pay attention to the money factor, ie. the interest rate you'll be paying. Those two things, plus fees, will determine the cost of your lease. Other things, like the residual value, are set by BMW Financial Services, so no room to play with that.
Residual on a 24/10 lease is, I believe, 64%. On a 24/12, a point or two lower.
I should think you ought to be able to get a transaction price discount, before the $7500 federal rebate, of about 10%, based on what others are doing. Maybe a bit better; there are a lot of dealers in New England, so there should be plenty of options.
You should 'buy down' the money factor -- each "MSD" 'costs' 1 month's payment (rounded up to the closest $50) and lowers the Money Factor by .00007 -- this money is refundable at lease end -- it ends up effectively paying you something like 15% on your money during the course of the lease. The BMW starting money factor should be .00134 before MSD's; don't let the dealer charge you more than this.
FYI, the Norwood, MA BMW dealer recently had a 2016 i3 marked way down; I think this may have been considered a used car, but I think it was a loaner? It might still have the $7500 federal rebate available on it? IIRC, the lease rate was pretty good, but I wanted a ReX model and needed to buy from a RI dealer due to a RI rebate.