I've just been to Llangollen and back and it is VERY busy - and not even the school holidays yet.
I agree with rgreg above. The Leeds-Liverpool around Skipton is very nice indeed, and you could take the Skipton - Settle - Appleby train ride before or after your boat. It's the Settle-Carlisle route (reputed to be the prettiest in Britain) but there's no need to go all the way to Carlisle. Appleby is the 'far' side of the Dales National Park, and is a nice little town to see for a few hours. Skipton Narrowboats may have availability? You could even hire a widebeam on that stretch. Pleanty of swing bridges as well as locks. If you went the other way, towards Leeds, you could see Saltaire, and 'do' the Bingley 5-rise.
Personally I'd avoid the Cheshire ring. A week is rushing it, and the middle of Manchester (the Rochdale 9) is an unpleasant experience.