The car is likely still registered to the previous owner and you'll need to call the BMW I-team to get it transferred, or possibly, the dealership can do it for you. Then, you should have full access and status on the car.
Often, failures tend to happen in the first year or so, and then, there's a lull for quite awhile until things wear out verses break. But, any foreign luxury car is expensive to maintain and a failure could easily exceed the cost of the warranty transfer. It's pot luck...think of it as insurance, without the factory coverage, you're self-insured. Sometimes you win, sometimes you lose.
Depending on how many miles you put on the REx, at a minimum, it would likely call for an oil and filter change annually. Other than the bi-annual brake fluid service (do not ignore this...it's from the date of manufacture, not date of first sale), about an $80-90 service at the dealer, there isn't much more. A cabin air filter and maybe an engine one, but you'll probably not get enough mileage to need one while the warranty is valid. They'll replace the wiper blades annually, and if you bought OEM ones, that's about $70 for all three. It's doubtful that the REx would need a tuneup.
2011 535i x-drive GT, 2014 i3 BEV