Thanks to Trusts, leveling isn't really locked to finding 5 others. There are other supplementary EXP systems like Records of Eminence and the Grounds/Fields books to help things along, too. So, in that respect, getting to 99 and subsequent Sparks gear isn't the hard part. Actually getting into Adoulin content, however, may be trickier due to a lot of people who play more religiously having it done already with little incentive to backtrack. This puts your luck more squarely on when you play and what job(s) you like to play. Coming from XIV back to XI may even seem a bit jarring without some of the more mainstream features of more modern MMOs like party finders.
Anyway, with a good job and sparks gear, you should be able to solo most story/mission content prior to Adoulin if starting on a fresh account. I probably wouldn't touch crafting since most desired items are just R/Ex in some fashion anymore. Farming for the more expensive spells for casters may be rough, so I'd perhaps advise a flexible melee class for your first go or even BLU since its spells are "free" in that regard.
Couldn't really tell you about the server states, just a presumption that they're likely similar. I will note I tend to see complaints about EU players having a rough time getting things down in their prime time, though. German and French support has also been dropped, but that doesn't much seem a concern. Registering a cross-region account may be tricky, though. Can't help ya there since I've always done NA from NA.
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