We stayed in a bunkhouse place, slept 6 but we had exclusive use. Dog made very welcome - will dog out the name. Dog was barely on a lead the whole time, the pub was next door and he just trotted in with us each night
Go out of main season - it'll be a lot quieter and even the touristy places are nice! If you are planning on climbing Snowdon then that goes even more so. It's packed during the summer and you can barely see the summit for the crowds.
I'm up in Snowdonia ( North) at the moment as it's our refurb week. Glorious run on the beach yesterday for ddog in the sun and we've just got back from a walk around the lake where we didn't see a soul.