YMMV, but I had a ton of fun 1-65 revisiting zones I fondly remembered from my original leveling up to POP. The novelty of revisiting some of those places wore off pretty quickly (COM, LGuk, Seb, Velks, etc.) as I started playing during late Kunark and didn't spend as much time there as many others. POP was really where EQ's story felt most developed and interactive, so I had fun doing content with the new defiant gear which was far better than the raid gear available in-era and got to see stuff I missed with my guild back then as we got to the ele planes at our apogee.
Resources:
Allahkhazam's is still good for basic info about the game and sometimes comments help you figure your way around bugs or weird mechanics. EQTC is my go-to for tradeskill recipes. EQ Resource is great for progression and understanding unique gear features in each expansion for which they have info. EQRaidLoot is a great database for loot and AA info. Adetia's tradeskill lists are great for masochists who chase 350 across tradeskills. EQ Progression is where I track epic progress and POP flagging (for Artisan's Prize). Redguides is just a great community and resource. I would not play EQ without RG's MQ.
My similar experience:
The new Serpent's Spine zones felt well done and minimized travel time as you level through one zone and move to the one next to it, so I'd use that for your new crew to catch up. Around 60-65, I spent a lot of time in POFire and bounced around a bit with the same confusion on where to go next, like you're experiencing.
Farm in DSH was a really great leveling camp at 65 (run the repeatable kill quests there as a bonus), then either minotaurs in zone or
gators in LP (easy, single pulls on the beach with no worry of adds if you're not in the path of the social frogs or bears) got me to 70+. After that,. Fortress Mech was a good zone for mindless killing. Once you're 75+, you could move on to the
SoD zones like
Oceangreen Hills, but you'll notice where previously you were slapping around yellow/white mobs, those will not be pretty challenging and you'll shift to white/blue depending on your gear. This is also the point where Defiant falls behind and by 80 you'll want to have transitioned away from it (e.g. Paragon from quests, Chain linked from HOT, T1 from HoT). From 1 - 7X, I always made sure to do the daily heroic quests that
@Redmonkey mentioned (from Franklin Teek) for a nice chunk of XP. Get the one for your level and the one below your level.
After that, the Underfoot expansion kicks off the modern era trend of 5-level expansion packs with repeating spells/skills and an on-the-rails gaming experience UF and especially HoT after it were gear checks on my group; getting T1 HoT geared was very gratifying (gear tank>DPS>casters/healers). The focus shifts to the storyline and questing rather than an open world, guideless experience from early EQ. From there on out, you'll focus on leveling and gearing through one expac at a time and moving on to the next. Once you're maxed on, you'll look to backfill various progression tasks for heroic AAs (merc & partisan quests), special AAs (DON), non-prestige augs for your non-subbed characters, and various other stuff. With 20+ years of development, there are plenty of things to do here and that's before you dive into optimizing your setup of MQ stuff.