Going from Llangollen to Barmouth.
Ideally I would chose April/May time, before the heather and tussocks have grown and you can still pick out some sheep trods and not fall into too many pot holes in the peat. If it has been dry it is far better underfoot, but no water and vice versa when wet weather, this is what caught me out, I expected to find water but didn't for the first couple of sections.
Whatever you do, make sure you cover the section from road at Milltir Gerrig to Bwlch y Groes road in daylight, don't hit this after dark. The rest is fine, also water after Bwlch y Groes.

If I was planning it again for solo (or with a mate) but unsupported and wanted an enjoyable day out I would do this.
Come down day before, drop water bottle and feed at minor road crossings and then spend the night in the van/car at Barmouth. Have early breakfast and catch first bus to Llangollen, run back. Really easy to arrange at short notice and you don't rely on backup supporters. Alternative would be catch evening bus back to Llangollen and night in B&B, then leave your overnight sack at accommodation to pick up later on return.

Just a few ideas.