Are critical engagements something you can queue for and get a group automatically, or do I actually have to find people myself?

I plan to play my Paladin, and I don't mind it being slower/more challenging to solo as long as it's possible. I mainly just want to be able to jump in and out at my leisure, and not need to be constantly reliant on finding other people in order to do anything.

Is Eureka soloable for the most part as well? I may try that to.