Well, you can always do Grounds of Valor pages in places where the monsters are low enough to be soloable to 75. That's been the way a lot of returning players have gotten their initial limit break done, or even their first two, and it gives you something to do while you build stones for Abyssea.
The typical way I've seen is to limit break 75, join an Abyssea party and level to 80 with 30 merits, then limit break, merit, rinse and repeat.
Also significant to note that KS99s are still worth decent money, and you can transform seals into any other seals on a 3-1 basis. So when you need the various Crests for limit breaks, just transform some Beastmen's seals.