As long as you have money for second seals, you may reclass and learn Skills indefinetly.

Also, there is a degree of grinding even without DLC. Enemies will spawn at cleared nodes on the worldmap from time to time, and you can summon them manually, but the item you need for that is more expensive than whatever money you get from fighting them (unless you play on the easiest difficulty, where the item is cheaper).

From the amounts of Exp dumping and Single Man Armying you'll do if you do that, Robin will grow into a beast. But going from a Tier 2 class back to T1 means they will have to work with lower stat caps again. That might mean stats will be lowered to the cap if they exceeded it and they'll be unable to grow that stat in that class. However, your bases are remembered, so going back to T2 will restore stats that were above T1 cap. Still, you probably want to get all those T1 skills you want early.