Advice Needed: First Moto Trip

For a four hour journey I wouldn't think too deeply. Just get on and ride!
My Speedy only has a small screen and those speeds you mention are easily handled, but if it's your first trip you may need to build up slowly and take a few breaks.
Enjoy your trip and many others.

 

The way to combat fatigue is to take regular and frequent breaks, alternatively drop the speed from 80+ to 60 or so and then the drag is much less and that makes for a more pleasant ride.

 

As a test a 4 hour trip shouldn't be too arduous. As mentioned you might want to get a build up daily plan, before the trip ride every day. On a multi day trip those aches and pains multiply each day. Work on getting "bike fit". Depending on how far from main routes you go carrying lots of spares might not really be necessary. I used to carry spares, tool kits, pumps, puncture kits and more besides. These days i take some zip ties and my phone, its got my breakdown services saved. If your bike is in decent condition it is not more likely to break down on a trip than its normal daily use.
i take one or two multiday trips a year, so whilst not round the world hardass, i have a little bit of experience, as general advice, and it has been said many times in many places and it is true. Get all your gear you are planning to take and put it out so you can see it all, then throw at least half of it away. Some things are truisms because they are true and this is one of them.

 

As others have said, I don't take too much in the way of tools or spares when I have a few days away on a trip like yours - bike tool kit plus a few extra spanners, allen keys, multitool with pliers and most importantly, my puncture repair kit (sticky string plugs), which obviously wouldn't help with tubed tyres, so you need to decide on that one. Would you attempt a wheel off repair or call for breakdown assistance?

I also have a few zip ties, bits of wire, wire connectors and insulating tape in a ziplok bag and a pair of plastic gloves to keep my hands clean if the worst happens.....

 

I didn't mean the bike easily handled the speed, I meant my neck and shoulders
Like everyone has said, have regular brew stops and you will be absolutely fine.

 

@Jamesian21: You may train your core and abdominal muscles. Then you are able to "work" again the upcoming airstream and in parallel you are able to relieve your arms/hands. The neck will also profit from this kind of training.
I was riding my former "Bonnie" with +80 mph for hours across some European countries without any issues. Don't forget get to take some refreshing breaks!