Chirk to Harlech is a rail to rail station line across Wales. It is about 55 miles longer or shorter is easily worked in around the start up the Ceriog Valley or on the Rhinogs at the end. Ceriog Valley to Llanarmon DC through the Berwyns via the Wayfarers gap to Llandrllo, up the Dee valley to Bala (either side). Lovely choice of ways up to Llyn Celyn, could knock of one of the Arenigs, big or small, then find the old Festiniog-Corwen railway track to Trawsfynydd (spectacular section of walk). Walk across Traws lake by the walkway (walking on water). Then you have a choice of routes through Rhinogs, my choice Moel Ysgyfarnogod to Clip before finding a way down to the coast and the Welsh coast rail line.
Hospitality in the way of interesting pubs all the way and camp sites. Well you will have to do your own route plan and navigate it, but I recommended it a few years ago to a lady (visitor to this forum) taking her 14yr old son on a first multi-day walk at got a thumbs up afterwards. Somewhere on a back post.