If you take a couple suggestions from someone who has been levelling chars from scratch on pretty much every international server and some French, I would only focus on one or maybe two characters first. I'm slightly biased but I would definitely pick the Iop for this role. You can get to 50 purely on quests and easy achievements in a very short time (zaapping around in Bonta and Brakmar alone gets you a level or two), then you can start grinding on whatever has the most stars.
Once you get some basic gear you can move onto Ouginaks or duo 60-75 Kanigers (leave the level 80s for now), take all the MP and long range damage idols, pick close maps, try to use a mount/pet with loads of Vit. Do the Almanax every day, class dopples are useful for basic scrolling, try easy achievements in low level dungeons. With a Sram and an Iop you can do monsters way over your level provided they only have close combat spells and not too many MP (Polished Cracklers, Yokai/Maho fouxes, Boowolves), though I found you still get the best XP on Ouginaks and Kanigers, which is slightly disappointing because they get boring quickly.
Make sure you make good use of idols, Dynamo and Horiz are amazing on aggressive monsters (especially with the synergy), Dagob for quick fights and even Domo and Payo if you are with your whole group.
Once you have a group of level 60-70 characters in something better than prespic you can do bigger Kaniger mobs (the joy), Dreggons, smaller Grassy Plain mobs. I don't know if you have any leftover kamas from the times when you played previously, if not, do the Wabbit Island questline, +60 wis is just what you need along with a couple more levels from the quests alone.
I remember certain mobs on Vulkania used to have a default +50% XP multiplier, not sure if that still is the case, worth a shot.