Best and least Crowed Cinque Terre Towns and trains to get there from Lucca

Corniglia is the least crowded ; it is probably the worst choice though if you can not do stairs and hills though.
Not sure I would look at anywhere other than Monterosso given that statement/requirement.

Don't think he would find any of the hiking paths easy or doable at all if adverse to stairs and such climbs.
Main trail from Manarola to Riomaggiore which is very easy and flat is not open currently, they are repairing it but will probably be a couple of years.

I have no idea to what extend his legs prevent him from walking hills, but in the CT it is hard to avoid stairs and hills.

For the most part the trains that stop in these towns stop at all 5 , they are only a couple of minute ride apart. I believe some trains do skip Rio Maggiore, Manarola, Cornligia and Vernazza and go straight to Monterosso but otherwise if it stops at any of the 4 it will stop at all 4. No one is easier in that regard but Corniligia is separated by a good sized hill between the train station and the town so you must walk the road, walk the stairs or take a bus and the bus gets very crowded.

I advise rethinking, as there is not an easy hiking path anymore (the easy, paved path was damaged in landslides). Perhaps you can enjoy a boat trip, but the crowds have made the towns less pleasant for day trips.
See trail descriptions and general info here:
http://www.parconazionale5terre.it/Eindex.php
http://www.cinqueterre.it/

virginia,

Most of the towns in the Cinque Terre are crowded these days, especially on days when the cruise ship hordes descend on the area. A few thoughts on the towns....

• Monterosso: this is the largest of the five and therefore has the greatest choice of lodgings, including more "conventional" hotels that also provide breakfast. Monterosso consists of a "new town" and an "old town" and *the terrain between them is mostly flat and very easy for walking.* It has the largest number of restaurants and other tourist amenities and also the best beaches of the five towns.
• Vernazza: In my experience this will be the most crowded, and the problem often seems worse as the town is very compact and doesn't absorb crowds well.
• Corniglia: this is probably the smallest and least crowded town, but also note that it's located on the top of a rocky pinnacle. The only way to get to the station is to walk up/down hundreds of stairs or take the shuttle van. There's less choice in accommodations and restaurants, given the size of the town.
• Manarola: also a very scenic town but when I was there last September I found it to be dreadfully crowded. There are some nice accommodations and restaurants there, but not in the same numbers as in Monterosso.
• Riomaggiore: also a smaller town, and accommodations are more smaller rooms and B&B's rather than hotels. Some will not provide breakfast. The main street runs uphill from the harbour, so your husband may not like that.

"Also is the hiking path easy from there to Manarola and then on to Riomaggiore."

Unfortunately you won't be able to hike on the Sentiero Azzurro trails either from Corniglia to Manarola, or Manarola to Riomaggiore. Both have been closed for several years due to slide damage and are not expected to re-open until next year. The trails from Monterosso to Vernazza to Corniglia are probably not a good idea for you, as they're more challenging with some steep uphill segments. There are other trails that go further up in the hills but those are a more robust hike, and probably not good for your circumstances.

The length of the rail trip and number of changes from Lucca will depend on which of the five towns you're travelling to. The trips to Corniglia seem to involve at least two changes, while there's one train to Monterosso that has only one change at Pisa Centrale. Travel time will be about two hours. Staying in Monterosso would probably be the easiest solution for your situation.

Whatever you decide, I'd suggest getting accommodations booked in the Cinque Terre SOON!

See additional responses on your duplicate post.