Also, once you unlock the travel ship, you can go to "ugly duckling isle" (3rd small island above Ding Dong Dell) and grind for Toko's (small and fast green creatures with staffs), they give a shit load of XP.
Once you reach Perdida, you can grind Toko tokos (they give even more XP)
Once you reach Perdida, you can grind Toko tokos (they give even more XP)
The Merit stamps you collect will come in handy quite quickly.
Also, once you unlock the ability to catch familiars, I'd go for a purrloiner (the pirate cat one) and evolve it to Puss in Bouts whilst playing with Oliver.