We have a 2006 Gulfstream Yellowstone bought used in 2010. We've been pleased with it thusfar. It came with manuals but, to be honest, I wonder worry too much about not having the Gulfstream manual - especially if you are already familiar with RV operation. It is pretty generic. You might be better served to find manuals for the specific appliances you have installed.
My biggest dislike is the flat roof. It hasn't caused any issues and I don't notice any puddling around a/c but that is always a worry. We store it at home and can see the roof from a second story window. I'll look at every so often after a hard rain just to be sure. It is parked a little off level which I hope helps.
The dinette was put together a little flimsy so I screwed in some additional supports where the back meets the sides of the benches. Basically, 3/4 X 3/4 piece of wood placed on the inside corner and screwed in from back & side.
As far as pluses, it has been a mostly solid rig for price paid. Ours is 31' and drives very good. I read many posts here of need to add steering stabilizers, etc. but I've not seen a need. We pull a 3,000lb boat and no issues towing except for occasional rear dragging.
Good luck with delivery and hope you get as much enjoyment from yours as we have with ours.