For multi-day long distance on a C5 I recommend the following:
(1) tall windshield: the air blast from an upright seating position, even a lowered one, is fatiguing for arms, back and neck. And while not as apparent, mental acuteness is reduced due to both physical fatigue and auditory fatigue. A tallish windshield will help greatly in fatigue reduction although its lines are not traditional RE and the wind load will be felt in the handlebars. Be that as it may, I recommend the Givi windshields, either the Universal (
http://giviusa.com/givi-products/windshields/universal-windshields) or if Givi has one for the RE and your budget permits the AirFlow (
http://giviusa.com/givi-products/windshields/airflow-windshields). I haven't used either nor will I ever put a windshield on my RE (although I love the adjustable windshield on my BMW) but I am favorably impressed by Givi design and production quality and from all the pictures I've seen of REs with windshields the Givi seemed most appropriate to your needs. Hopefully other forum members will jump in with their specific experiences.
(2) tranquil handlebar: there are two major sources of "noise" from a motorcycle: audible and physical. The majority of physical noise on an RE are hands and butt (feet aren't too bad at least with good boots). WRT hands there are two major aspects: the handlebar and the grips including gloves. WRT grips I assume you are using Grip Puppies or something similar. WRT gloves something like my thin elkskin gauntlets are inappropriate -- great road feel but you want more palm padding and finger wind protection. WRT handlebar, you want DEAD. I suggest you buy an open-end handlebar and fill it with lead shot per The Old Coot (
https://forum.classicmotorworks.com/index.php/topic,21998.msg247873.html#msg247873). I'm doing that with my RE and when I'm done I'll let you know how much lead shot is required. If you have the Halycon or similar HEAVY bar end mirrors you don't need bar end weights. Any other mirrors you should also use bar end weights.
You are less than half my age (I'm 72) but a physical and mental training regime is mandatory. I assume you are researching Iron Butt and similar rides in Cycle World, Motorcyclist, etc. You should also research road racing. When I send you the Spark Nano I'll include Keith Code's A Twist of the Wrist. Mentally and physically your journey is like road racing from a dl/dt perspective. I ride 100 miles/day at least 4 days a week without fatigue (don't ask about stiffness). You should be riding at least twice that minimum. Plus a 500 mile trip every week. Remember you will be doing that every day for at least 4 days according to the schedule you've provided us so far.
WRT diet while on the road, boring is best. Choose a consistent, limited meal repertoire. That all-you-can-eat hot links and ribs special is tempting but your focus is the road. DON'T LOSE YOUR FOCUS!
One last reminder. If it hasn't been apparent from other forum member contributions, the human element (that's you) is the weak link not the machine (that's your RE) in this adventure. We want your success.