I have a Givi Trekker, think it's a 46L, got it originally for my 650. Not done any overnighters so can't comment on combined capacity but like yourself I have a dry/roll bag if not. I think it matches the stock panniers (they aren't big enough to warrant both n's) well enough and let's face it, it's behind you so you don't see when you're on the bike.
I have the Givi Airflow screen, works for me. Seems to be the best choice all round. I had it swapped out before delivery, just couldn't get on with the stock screen.
I'd second John's recommendations of hugger and side stand plate. I have neither as of yet but both are on my must buy soon list. Having seen them both of them on Johns bike I'm happy to go with the givi hugger/R&G plate. Just need some funds top up and I'll get them ordered up.
I'd also think about replacing the stock exhaust can. Apart from the aesthetic aspect it's reputed to make the engine run that bit more freely (although I've never run the stock can so I could be talking out my arse). And let's not forget how it sounds....
Hope you enjoy the bike