I cannot be certain about the lease return policies. I suggest you call the local dealership and ask somebody there. It will be a very short conversation - yes or no question. You can also speak to a Lease-End Relationship Consultant by calling 1-800-959-4BMW (4269). If I were to guess, I would assume that you can return it anywhere, since the car will actually be property of BMW Financial Services, and not the actual dealership.
Regarding the monthly payments, there are really too many factors to consider. I recommend that you "build your own" 325xi on bmwusa.com: http://www.bmwusa.com/byo/byohome.ht...=XAB60BMC142A0
And then click on the "calculate a payment" link. I was going to do this for you, but there are too many different options that would affet the price. Since you will be making a lot of money, and seemingly are ready to spend it freely, I assumed you didn't just want a barebones 325xi with no added options besides the navigation system.
Last week I checked what the price would be for one with a few options tat I like, and a manual transmission. The sticker price came up to about $39k. I will assume that one to your liking would have a sticker price of about $43k, and would incur payments of $613/mo for a 36 mo. lease, $2500 down payment, and 15,000 annual miles.
The following link may also prove useful: http://estimator.bmwusa.com/estimato...eConditionId=1
I find it curious that you say that "any help would be much appreciated," but you seem to have a negative reaction to miztuhdan's reply, in which he clearly stated "however I'm not sure so don't take my word on it".
That person answered both questions:
I do believe you return it to the leasing dealership
for a 06 325xi, you'd be looking around $750/mo, supposing the 325xi is completely loaded