A BMW 535. The only “nice car” I’ve ever owned in my life.
The N55 is one of BMWs most reliable engines, if maintained properly which it sounds like your former company took care of. The ZF8 is one of the best transmissions on the market and used by dozens of manufacturers. The biggest maintenance issues are oil and coolant leaks, which when addressed early are not terribly expensive. The electric water pump and cheap plastic expansion tank are pieces of **** though and depending on driving style/conditions/mileage can cause headaches every 60k miles, moreso for someone in the southwest than someone in Chicago. One of the reasons BMWs have such a bad rap is the original owner leases, the next owner buys because of depreciation but can't afford to keep it maintained and things snowball until they have $5k in deferred maintenance, so they unload the vehicle and it becomes someone else's problem who sees the $10k pricetag and thinks they are getting a screaming deal. On the enthusiast forums and FB groups there are plenty of people putting 200k+ miles on older BMWs, although they do most of the maintenance themselves to save money.
Also the F10 is a good looking BMW with classic styling. It is no E39, the pinnacle of BMW design, but they got rid of the Bangle butt and scrunched front end from the E60.
As for the check engine light, Autozone and O'Reillys can pull codes for you but they are generic codes and do not include all of the specific BMW codes. It is a good place to start though. There is a good chance it is the O2 sensor, which if I remember correctly is around $1k to replace at the dealership, probably less at an indepenent shop. They have a front and a rear though so if both are bad that could be double.
If you are only driving 5k-7k miles a year you could keep it running for another 5 years or more with minimal maintenance cost assuming everything is up to date, other than an oil change once a year and a new set of tires at some point. Much cheaper than a new $500/mo or more note and more practical in my view given the amount of driving you currently do.
A pretty decent resource if you don't want to hassle with FB or forums is the r/BMWTech subreddit, dozens of questions are asked everyday and answered by actual BMW Techs, BMW enthusiasts, and YouTube mechanics.
www.reddit.com