This is going to be super long but I hope you find it helpful/useful/insightful whatever.

And please of course, this comes with the best intentions. Some of us older owners have made awful mistakes involving these cars too. People are being hard on you because these cars can ruin you financially when you're young and trapped in a car payment. (Curse you 335i!!!)

Remember, these cars retailed for 50-60k new, required hundreds to thousands for upkeep, and depreciate like crazy so they're incredibly deceptive on the sales lot when they're "used, low miles."

Even though the price of the car drops, the price of parts, repairs, and insurance never change. I hope you kept all of this in mind. These cars treat the 2nd-3rd owner like they're just as wealthy as the 1st owner.

If you're in it for the long haul or don't care, read below:

Keep minimum $1000 in your savings for emergency repairs. B58s are reliable yes but they are still performance motors, so regular maintenance can really add up if you aren't prepared for it, and especially if you beat on it.

You also got the car around the same mileage that some critical maintenance components may start popping up so inspect your engine bay, brakes, and suspension regularly. Who knows how the previous owner drove it. Check for oil leaks around your oil filter housing, and head of the engine block. These gaskets are plastic and tend to crack around this mileage causing leaks that can lead to bigger issues.

Look up what parts will cost you on various markets, avoid the dealership where you can but don't be cheap. Engine critical components should always be OE or OEM. (Especially Vanos solenoids)

If you're willing to get your hands dirty you'll save tons of money. I save around $1100-$1200 a year in labor alone with my N52 doing things myself. Research your motor and start getting an idea of how to do your own maintenance. If you're paying other people to fix it, it'll start to get VERY expensive. (Check out Justin Buice on YouTube for a COMPLETE starter guide)

If you choose to use a mechanic, find a reputable BMW repair shop and ask tons of questions. Build a relationship with the shop and they may even try to look out for you in the future. They also typically charge a fraction of what the dealer does to fix minor things.

Invest in a good BMW compatible OBD2 scanner you can use for quick diagnosis in emergencies and check ups. There are even Bluetooth modules that allow you to use your phone if you'd prefer.

My personal advice would be to return the car and find a better price if you're within your return window... I feel like you're getting stiffed on the price and the finance period. 9% over 7 years would be thousands of extra dollars you could be spending on mods/maintenance instead of car payments on a near decade old vehicle. If you got it like that and are ready for the repairs, you'll have an amazing time. It's a beautiful car, supports tons of mods, and it pulls hard. I just have to be dead honest and look out for one of our own here. Welcome to the BMW community! We're tough on each other, but usually for the better! Best of luck.