I put a very expensive seat (don't recall the maker at the moment, and paid $50 because I guy found it lurking in the garage a decade after the bike was gone) on my '04 BMW GS Adventure. It's better than stock, for sure, but I did 10k on that and the stocker on my '97 1100 Sport-i and I'd take the Sport seat every single day over the 'nice' beemer seat. The bucket is better for the first 3 hours, but then becomes constraining and I can't shift weight away from the contact points. As stated, on the centerstand it turns into a swimming pool. (not that you can get a GSA on the centerstand) Everybody gets their opinion on that, and miles matter.
Leather is best, but *must* have Mink or Saddle oil.
Bicycle shorts are an absolute must. I wear Underarmor in my riding suits, because they already have padding but I wore bicycle gear under jeans for years.
Don't forget your Thorlo synthetic or Hollow Alpaca boot socks and Gold Bond foot powder.