Thank you all for the very valuable comments! I wish there was a way to respond to you individually, but it seems it's not possible on this forum type. And so..
dmr: yes actually we were initially thinking about a 4 week trip originally to be sure we could really relax, but as you say, we'd be committing to a long stretch, plus, there's the cost. I'm again thinking heavily about a longer trip per your comments, also the longer boat for comfort on an extended stay.
David: Not really needing to do the 'American tourist thing' we're more inclined to spend some time getting to know a place vs. checking off places, we did that approach while younger 🙂The S-U canal sounds promising esp. based on some of the vloggers..
Agg221: another vote for the four counties ring so that's moving up the list. Yes, we'd like to do the semi- trad / cruiser stern so the boss and I can both have a place to rest our bacon while enjoying the stand-up view! Not too keen on Birmingham based on some comments of safe places to moor, but excellent comments on the side trip scheduling.
howardang: You're one of multiples citing the four counties ring so that's hopped to the top of the list! Hadn't considered multiple hires, but that's worth investigating. Would need to figure out the logistics of packing / moving to a different vendor but could be adventuresome to do two different legs / vendors...hmmm..
dorathexploere: An alternate view from the four counties! Say more about longer locks being potentially less hassle than the smaller ones???
manxmike: Thanks for the Black Prince recommend; we've been looking at them as one of the bigger vendors. Might also be a good idea if we decide to do two different canals with a boat switch between, and still get the volume discount via a single vendor. Another vote for four counties ring.
pomkitanner: Great observations regarding comfort as we're back to planning a longer trip. Not too worried about the bench seating vs captain's chairs but we are used to a king size bed and 4 weeks in a simple double might have one of us (me) sleeping on the bench after a few days. Esp. if I might have a cigar and / or a glass of red wine. (snore like a chainsaw..)
shroudwater: The G-U looks wonderful on the vlogs as well and has lots of potential per a post/pre stay in London and a hookup with friends there and in Cambridge. Not sure I'd want to try the Thames or Wey in a narrowboat for my first outing, however.
IanD: Thanks for the second comment on comfort; has me thinking again...
Again many thanks all, you've given us both lots to consider and more research to do! I'm sure we'll have more questions as we go along.