Welcome back to the game! Lots has changed since the 75 era. Lots of opinions about that but what’s certain is that there’s probably some content out there now that you haven’t experienced that you’ll have some fun with. Enjoy!
For linkshells, SE made some new npcs that distribute linkpearls for recruiting linkshells. The linkshell leaders put pearls on them to distribute to others. My recommendation would be to pick up a pearl or two from one of those npcs and ask around for people to play with. In my experience, people are not nearly as selective as they used to be during the era of 75 shell rivalries. In fact, you can equip multiple pearls on your char now.
https://www.bg-wiki.com/ffxi/Linkshell_Concierge
In terms of stuff to do, why not start with getting to 99 and knocking out this list of record of eminence objectives.
https://www.bg-wiki.com/ffxi/Category:Records_of_Eminence#Intermediate