heya, no you totally don't need plat to get ahead. My rogue got to L15 without spending any plat and i didn't spend plat on my mage until like L13.

The party you're with makes a much larger difference in terms of how they handle the boss fights.

I think there's a bit of a difficulty spike for the boss fights on the third and fourth maps. After that it's ok as you figure out the game and what skills work for you.