They are between 17 and 18 lbs - very light for 17's.
They are cast but known to be very strong. BBS RK's were run on many Speed World Challenge cars, and are often seen at track days. RK's in E36 + E46 offset were recently discontinued, but so many people clamored for the return of the RK because of the rare combination of light weight, strength, and affordability, that they were subsequently re-released in that fitment.
I'll trade you my 16" RKs!...haha I might even trade you both sets that I have. This is my opinion, but those 17s sure look a lot better than the 16" version. I didn't think that 1" in diameter would make such a big difference on the look of them, but they do. Great looking wheels.
Sure. (Car looks like this now, just different front plate). Notably mine are the polished finish RKs, the ones you're selling are the silver painted finish.