Meteora

I case you would find the walk too long, you could always hitch-hike for a part. Almost all cars you will see there will be driving the loop, many of them will be tourists in rental cars and they will all understand that you need a short drive.

Each monastery will have toilets.

I would strongly advise to stay in Kastraki. We stayed in Doupiani House, a guesthouse just off the main road towards the monasteries, on a quiet location with wonderful views.
Kastraki is small but it has some very good tavernas.

Thank you all very much for taking the time to reply.

Your information was very helpful, and I am especially encouraged to hear that I can take a bus to the top and wander down from there. It's definitely on my itinerary now!

Thanks again, and happy travels!