Welcome!
The K75 engine, when maintained properly, is stone reliable and very smooth running. You can literally run it at 70+mph all day(24 hours). I know because I've done it. A properly cared for brick will easily go well over 150,000 miles. 40 to 50k is considered the break in period.
Parts are not that much of a problem. If you need new, MaxBMW sells at list, but doesn't charge sales tax or for shipping. Also, because of a lot of bikes being parted out these days, there is a plethora of used parts on eBay where a little shopping can often find good deals. If you have a few tools and aren't afraid to get your hands dirty, there is a ton of good information here and on the web that will get you through pretty much any problem you might have.