Will I be able to have more Crystals and Health as I level up?
The maximum amount of Crystals and Health does not change as you level up. These values only change when your whole class moves from Chapter 3 to Chapter 4 — that's when you unlock Health!
Guardians, Mages, and Healers have unique strengths and weaknesses, including these stats. It's important for you to work with your team! Guardians have few Crystals but a lot of Health, Mages have more Crystals but their Health is lower, and Healers are somewhat balanced.