My best advice would be to level your team in the festival grounds during the fest. The area's enemies will be at the same level as your highest level pet. So it's a great way to level up without having to go to an area that may be too high for you yet, or trying to level in an area that's too low since you won't get much experience in them.
Just make sure you have all 3 slots unlocked and filled before going to the fest grounds and you should be good. ^-^

Thanks!

I will try that.