If it were me, at a minimum I'd replace every seal, including the valve guide seals and the VANOS seals, starter, lower coolant tubes (along the block under the intake), CCV system, and clutch no matter what. Age is a factor as well as mileage, and BMW rubber seals are not known for their longevity. As to the rings, well, as noted a leakdown test might help you decide whether it's worth the cost and effort. They don't wear out, they break, so it's not just a matter of mileage.
Again, the M54 would not be my first choice. Frankly, I'm not a fan of engine swaps in these cars period, but that's just me. No matter what you do with the M54, just be aware of its weaknesses.