Welcome to the game, it's a good time to try out a few things.

I recommend running those leves you picked up, they are really good for leveling. And once you hit Rank 5 (not level 5) a new camp (Camp Skull Valley) will open up, and you can pick up more leves from there.

Some of the starter leves will reward you with the starting weapons of different classes, so you might want to look at those and thus not have to buy from the shop.

Quests will reward you with money, gear, and SP, so when you aren't running leves (think of them as dailies) they offer a good progression.

The reason you will want to level other classes is that abilities (some not all) are cross class, so say you pick up a wand to become a CON, you'll learn fire, ice, etc... and now when you switch back to PUG you can equip those spells (if you have enough action points) and be able to cast that spell. This comes in handy when building the role you want to play.

Soon more adjustments will be coming, I suggestions posting your feedback to the dev team as they are listening.