Having learned to fly at Welshpool, the Welsh hills were pretty much my local area and it never occurred to me - or anyone else from Welshpool
AFAIK - to file a flight plan. However, it can't do any harm, and some of that area is quite isolated. I'd agree with what everyone else has said about the weather; it's quite rare to be able to fly over Snowdonia without either cloud or strong winds...but the coastal route is beautiful too. As for the radio, I've never had any problems getting hold of London Information, or using Liverpool when near the north coast. Have fun; it's a lovely area to fly in.