I've got a 2001 1150GS with 50,000 on it and love that bike like no other I've ever owned. It's a fabulous machine, but I must admit mine is a tad dirtier than the one you just bought
. I wonder what I'd have to pay Curt to come clean mine like that??
I wouldn't worry about hurting the original plastic hard cases, I've bumped and bashed mine many times and they've got battle scars but have never failed, never leaked, and never cracked. I had the seat recovered by a local upholsterer to add a layer of dense memory foam and a waffle-weave cover for a bit of additional grip and air flow, but otherwise the seat is fine for my skinny butt. Get good riding pants and use bicycling shorts underneath - moisture is your enemy there more than anything else. For long trips I have sheepskin pads for myself and my wife which are wonderful! No need to drop a wad of cash on a seat unless you really find after a bunch of miles that it doesn't work for you. When I first bought my GS I also had an 1100RT and a K75 (plus several dirt bikes) so that's mainly why my mileage on the GS isn't higher. As I write this, all those other bikes have been sold but I still own the GS; it's just the most versatile bike I've ever owned and I love the ride, ease of maintenance, and bomb-proof nature of the thing. You can load it like a moving van and it still handles beautifully; pull all the bags off, take the pillion seat off, and go do some fire roads. Excellent machine!
The one thing I saw in those photos of your new bike that would concern me are the brake lines. If it still has the original lines, you should replace them ASAP. Here's why:
The brake lines are the only thing I've ever had fail unexpectedly like that, but what I now understand is that they were considered a wear item like the alternator belt or crown seal. They'll go a long, long way, but they eventually wear out. Kinda spooked me how bad they were and I never knew it.
Take care, I think you got a nice bike for a reasonable price, now go see if you can wear it out!