Is 258'700 kilometers(160'313 miles) allot for a 1996 BMW 735i V8 (so rather large motor) ? Petrol not diesel

In general, that's a fair number of miles in total but appropriate for the age (actually low for the age if you figure 15k miles / year).

But BMW's are known to run over 200k miles. It all depends how the engine was treated. At this number of miles I'd plan for (set aside $$) some repairs. They will most likely be to sensors and not to the core mechanicals, but stuff is going to wear out. Expect to replace /repair things on a car this age. Realize that BMW parts and the labor to fix will be more than if you owned say a Honda. (I owned 99 BMW and 97 Honda at the same time. PCV valve for Honda $5 and 10 minutes of my time to replace. BMW 528 PCV valve cost $49 plus $500 labor in california. I could not do it myself.)

You might get a pro mechanic of your choice to evaluate it. They can do a compression check on the engine and give their opinion. The V8 is a little more trouble prone than the 6 cyl. partly because it lifts up a bit and can/does break the radiator (plastic) fitting off (in the 97 740 at least). There are a lot of plastic parts on BMW and they seem to decay on me. But you can replace many of them yourself.

Don't ignore the trans. It has also got 160k miles and just as expensive as the engine. Trans are NOT known to give problems

Ask to see repair records. Ask if the water pump, brakes, hoses, plugs, Oxygen and Co2 sensors have been replaced. These things will eventually need replacing. The 7 series is thought to need new tie rods by 95k miles, but if the car drives nice and tight you are fine.

Net, net, I love my BMWs but they are more trouble than a Honda or Ford. And you can frequently fix it yourself if you are willing to search the internet and BMW forums. There's a lot of help out there.