Just be aware and know what the problems are and try to prevent them.
Simple oil analysis is a great starting point to know the condition of the engine. If the analysis is positive then there isn't much to worry about when it comes to bearings.
Saying that I would be swapping the rod bearings and the engine mounts between 90-100k simply because it makes sense to do both at the same time. Depending on age I may have the mounts changed earlier as these cars are 10 years old and the mounts are rubber and tend to perish, its not easy to see the condition of them from the top of the engine bay, as they tend to crack and perish towards the middle and bottom which you can't see form above and you have to take the engine shield off to get a good look. They perish because.. rubber perishes and also from heat as one side is only a couple of CM away from a heat shield.
Many people don't know that rod bearings are a wearable item and should be put into a maintenance schedule if the car is getting to high milage, they are generally warn faster because of cold ragging as the car doesn't have a dry sump so the oil can get starved and creates more wear, another sign is metal particles in the oil which will be shown in an oil analysis. Problem is not many BMW dealers know this and its not technically in the service schedule but like anything its a wearable part and is the most likely culprit of an S54 failure.
2k should get that job done parts and labour and if its a keeper then its a price worth paying not only for piece of mind but the car will last into the 100s of Ks if looked after properly.
Another issue is engine bolts, just have them checked and changed if necessary, not stupidly expensive. Pretty obvious when you have this problem as the engine gives a faint rattle and if serious the engine drops and you get a loud grating noise which will cause a lot of moneys worth of damage.
Other than that oil changes regularly and have someone you trust to work on the car that can tell you everything you need to know, Get a full inspection of the vehicle and sort any issues, people are scared to spend £2-300 for a good check but it will save up to £7ks worth of damage. Get a look under the car and let them go through it with you, really reduces the worry.
Its all about preventative maintenance and knowing what to look for, otherwise the car is pretty bulletproof. Even vanos rebuilds arent insanely costly but they are fairly rare anyway and again vanos rattles are obvious as the tapperty sound of the S54 is no longer tapperty but very clunky.
Many of these items are getting cheaper because there are many cars on the road that need it, M3s pushing 15 years old high milage and people who want to keep them on the road. Now the Zs are at 10 years+ FBMWSH is still important imo but I would have a specialist do these jobs as they are probably the master mechanics of these cars 10 years ago now all these mechanics are only taught to read a computer it makes them a liability on these older mostly mechanical engines.
Luckily compared to M3s barely any were sold and most buyers are not yobs so its much easier to get a good shape Z4M compared to an M3 also the reason the insurance is about half the price, although they are the same on paper.
Enjoy it, drive it, look after it and spend the money on it.
It sure has all the stamps from BMW though. 
