Game mechanics wise, I'd start by working up what is likely to be the two sub-classes for SUM and SCH, CNJ and THM. That way you'll be able to take Arcanist right to 30 and go SUM/SCH as soon as it's available. Arcanist Guild is in Limsa Lominsa, so I'd avoid doing those quests.
Character wise, I'd perhaps have him be studying magic, but with a focus on the particularly odd magic the Beastmen use. That's where the summoning ability seems to stem from, so perhaps have your character notice it in their travels and start trying to unravel the mysteries of it all. When it gets close to release, have him start making breakthroughs in his studies that lead to him being able to bring forth Carbuncle.
Unfortunately, I haven't seen any lore about just how one BECOMES an Arcanist, so... maybe someone else can help you with that part.
Character wise, I'd perhaps have him be studying magic, but with a focus on the particularly odd magic the Beastmen use. That's where the summoning ability seems to stem from, so perhaps have your character notice it in their travels and start trying to unravel the mysteries of it all. When it gets close to release, have him start making breakthroughs in his studies that lead to him being able to bring forth Carbuncle.
Unfortunately, I haven't seen any lore about just how one BECOMES an Arcanist, so... maybe someone else can help you with that part.
My life is a chip in your pile. Ante up!
