Quality bibs are huge for me. Some dont care what bibs they have, but others really notice a difference. I am in that second group. I have been given a few pairs of PI bibs as gifts and have returned all three because I dont like them nearly as much as what I use(Voler Black Label). There are a ton of bibs, and the cost is so wide ranging its tough to figure out what the sweetspot is between quality and cost. And that sweetspot varies between people, which makes it even more difficult to assess.
If you can, buy 4 pairs of bibs from various brands, try them on, and see which is better. You wont be able to actually test them on a bike for 2 or more hours, but even trying them on can help determine if you like or dislike any of the bibs. Features like having straps that go around the nips instead of over the nips, or a low front cut instead of a high front cut(peeing is easier), or how the leg band is made(thick cheap silicone band or quality 4" compression band), etc. It will cost $600 in the short term, but you can then return what you dont like and keep what you like(if you like any of them).
Pearl Izumi, OrNot, Eliel, Voler, Gore, Rapha, etc- there are a lot of quality brands that offer bibs in varying cuts since we are all different shapes.
Hydration is obviously important. If you can, add something to your water to help replace what you lose thru sweating and exercise. nuun tabs or any of the similar products, for example.
Nutrition can be tough to care about since it seems like my brain doesnt send hungry signals while exercising hard or for a long time. But as soon as I stop, my brain is like 'why didnt you feed me?!'. Having Cliff blocks while riding helps- its some calories and it is something to do during a long stretch of nothingness on the road. Other small prepackaged energy foods are similar- try to have one every hour or whatever you think is needed. Heck, a small bag of cashews from home works well too.
Sleeves are helpful. Amazon off brand sun sleeves like these Aegend branded ones are, for me, just as quality and lasting as any cycling branded sleeves.
https://www.amazon.com/aegend-Pairs-...04&sr=8-1&th=1