Don't overpack. If you're going for a week and not camping and have managed to fill 80 litres of luggage you've got too much stuff with you. Take only the clothing/toiletries you really need. Many toiletries come in small sizes which will save a bit of space. 40-50 litres of luggage space should be enough for a week of touring. If you're not used to riding long distances you may want to do a long test ride before you go touring and do it for multiple days in a row just to see how comfortable your bike really is. I have found that the Ducati touring seats improve comfort massively. Also wearing padded cycling shorts under your leathers will improve the comfort. In hot weather it will also make getting leather trousers on and off much easier. Wear layers of clothing. Depending upon where you are going you may encounter a range of temperatures and weather in one day. I have ridden from over 20 degrees to close to zero in the Alps in the space of a few hours. Having layers that you can easily remove or put on will make coping with weather changes much easier. Bear in mind that if you are heading south the the coldest bit of your journey may be your starting point. Just make sure you leave enough luggage space for the layers that you will shed as you head south. Make sure that you take tools for all the minor things that you might need to do such as tighten mirrors or other bits that may come loose, chain adjustment, etc. I have needed to bleed the clutch on several occasions on tour. If you are travelling in a group you can share tools to save some luggage space. If you are touring in a group have a long enough cable/chain lock that can lock two bikes together. It doesn't need to be the heaviest chain in the world, it's just a deterrent to stop your bike being lifted into the back of a van.
If you have never ridden 500 miles in a day before, the last 100 miles will be torture. But once you have done it a few times, it will become easy. 100 miles over high alpine passes = 200 miles on ordinary terrain. Allow enough time.
If you are riding long distances you will find it much easier if instead of focusing on how far you still have to go to your destination just focus on getting to a town 20-30 miles away. On a long journey don't try to ride for a long time without a break. Usually fuel consumption dictates stops, but depending upon the bike and the roads you may find that you are able to ride for 3 hours before needing to fill up. Regardless of the need for fuel stop every two hours and give your mind and body a short break. This will keep you more alert and comfortable on the bike and enable you to ride for longer. A long journey is likely to take about 4 fuel stops. It is the penultimate stint of the journey that is usually the hardest mentally. The final stint is ok because you know that you are closing in on your destination, even though you are physically tired.
Don't get distracted by the road side prossies in Italy and nearly rear end your mate........'A friend' told me this piece of advice....
There’s an old Chinese proverb saying something about the stops along the way are what the journey is about, not the end destination. Get off the main roads & enjoy scenic routes & don’t go everywhere at top speed. You’ll miss all the interesting stuff. And pack a couple of pots of Marvel Milk powder. It’s the best thing you’ll ever do
Stay hydrated, At every fuel stop drink 500ml of fluid and buy another bottle/can to keep on the bike.