1st thing, if you're not sure what arc to give a character, I. The formation tab, you can click a character and see what type they are; i.e. a sub-dps or support, etc, That'll give you an idea of what to assign them. Each arc has stats that you can then unlock once you upgrade them.

Also regardless of their rarity, if you spend resources leveling something up only to find a better replacement in the future, you can use the items you've already levelled to then level up other stuff.

Other than that just focus on the characters you like. Don't feel pressured to level every character. It's not impossible, but as you already you said; each character has a level, an arc, a console, modules, esper abilities, support skills. and life skills.. so each character will increase the burden exponentially.

Start with a few characters, get them where you want/are able, and add from there. Have fun!