Demos/loaners qualify for all new car incentives until 5,000 miles and are discounted more than truly new cars with near-0 mileage. The residual takes a hit based on the mileage, but it’s usually still cheaper than non-demo/loaners.
Check out the Marketplace threads for current broker deals. These offers are likely better than anything you can negotiate with a dealer on your own. Just make sure you are comparing apples to apples. The deals listed by brokers often assume tier 1 (720+) credit and some incentives like loyalty, which you may not qualify for. They may also include fees, taxes, and MSDs whereas dealer offers typically do not. The fees may also differ from dealer to dealer. The offers on dealer websites are terrible compared to the deals offered by brokers here. It’s not impossible to negotiate a good deal on your own, but I would recommend going through a broker if you aren’t very experienced in lease-hacking. Especially if you live in NY where MSDs are not allowed, going through a broker to get a car from NJ is probably worth it. Max MSDs vs no MSDs on my 330i was a $900 difference, for example.
Also check out the Share Deals & Tips threads for real examples of recent deals.
For BMWs, warranty is not a concern for 36 month leases since it covers 4 years/50,000 miles. However, the free maintenance plan is transferred based on the original in-service/title date of the vehicle. So if the vehicle was in use for 9 months and 4,000 miles, you would be left with 27 months and 32,000 miles. This shouldn’t be a concern since the plan (BMW Ultimate Care) basically only covers oil changes and air filters. The oil change interval is 10,000 miles.