As David2386 said, EI-DKG of Eirjet has operated for EZY at LPL for a while now and has done the EZY618, which I believe you are returning on. Regarding the outward flight, some days it is A319, others B737.
Yes, those numbers will be your booking reference (I’ve got one here which is 7 characters long). Just print out the page/email you get and take it & your ID to the checkin desk.
I was under the impression that Ryanair were withdrawing from Sweden, so the Stockholm route is a bit of a surprise, but the other two have been in the pipeline for quite a while. I’m interested to see what price the Canary routes will be.