Rev lights can be configured in a sub-menu somewhere: ignition on, neutral, engine running (I think). Flick mode mode until menu appears, select it and follow the menu options. Dealer may reset it at service. I just have mine coming on at 7.500. Yes it likes to be revved.
Surprised at your comments on the rear brake. If anything mine is too strong, but it is an earlier model so maybe they changed something.
Screen, very personal thing. I don't find mine turbulent but it is noisy. MRA deflector wing thing is a good addition. I bought a package of used V85TT accessories recently that includes a massive Calsci screen. Not fitted it yet and may not like it when I do. If so it'll be up for sale.
Seat, again personal but we both find the high seat we have on mine as about the most comfortable seat on any bike we've had. My last bike - a 1200 GSA - had sergeant a seat we did ens of thousands of miles with. The guzzi is more comfortable than that. But like I said, personal.
Noise, yes stock setup is very quiet, yours possibly even quieter being a Euro5 bike (mine is E4). I have fitted a full Mistral system bought in stages: De-cat Y piece adds a good bit of sound, and loses weight and heat. Various option on silencer but I went for a Carbon Mistral can as I liked the look. A lot of people just keep the standard can as its not that muffled. Then I added the big bore headers. VAST improvement in sound and I am sure a noticeable improvement in low down power, but extra noise can be deceptive. Oh and then there's the V twin boost gizmo fitted with the Y piece (fools the intake temp sensor into a lower temperature so it richens the mix). After all that the bike definitely more tractable, sounds better and pinks less (they all seem to pink when hot and going slow). Fuel consumption dropped from low 60s to high 50s though.
Luggage - I have the standard 3piece MG hard aluminium luggage. It fits well and is well made but a tad small for two of us. The package of accessories I bought included a Bumot pannier set so I'll be giving them a go soon. Which means my panniers and frames will probably be up for sale before long. At this stage I expect to keeping the top box.
If they aren't fitted the standard Guzzi crash bars work well - I know from 55mph slide down the road. They are only about £80 - great value and easy enough to fit. MG heated grips are over £200 and I eventually bit the bullet and got some after farting about trying to make some old Oxford ones fit. The wiring is there waiting for the grips to be fitted and are controlled from the little white button on the left hand bar. The fly by wire throttle does need a bit of recalibration (dealer job) - its ok for normal riding but if you want cruise control the increased radius of the heated grip makes the throttle too sensitive and it knocks of cruise waaaay to easily.
Caponord front mudguard is a direct fit for extra front end protection, decal kits available from some guy on Facebook. Make sure you get the Capo Adventure mudguard.
They are great bikes. I'm on 13,500 miles and it still scrubs up like new and the engine seems to be getting better and better.