I find the standard screen terrible, loads of buffeting and dust in my eyes with the helmet flipped. I just bought a Slipscreens DB screen, bargain at £40 inc. delivery, will post my thoughts when it arrives.
As for the seat, don't be in a rush to change it. I honestly don't mind it, find it comfortable even, but it depends what you're used to I suppose. Off the shelf replacements are just so expensive and the results are so subjective. It might be worth searching out a trimmer locally who can do something custom for you if it starts to be a problem.