Cinque terre

Yes, CT is busy with day visitors till end of cruise ship season (October?)
The villages are very close together. If you just want to walk the main route between them, it can be done in a day at a relatively easy pace. The villages themselves are very small and don’t take long to visit. There are other trails that are longer and harder. My view is that 5 days is probably too long for the area. Maybe three days at most.

Stay in one of the villages or at somewhere like Levanto, just north of the villages; it has a good selection of hotels and restaurants. There is a train service from Levanto to all the villages.
La Spezia is a busy port and is the stop for all the cruise ships headed for the CT.

Have you looked at the website for the CT National Park? Full of useful info., particularly with regard to trails that are open, etc.

1. In early October 2022, the C.T. area was uncomfortably busy, so I’d imagine that September 2025 will be even more so. I don’t think I’ll ever bother going back there again, but if you haven’t been, go if you want, but expect mobs, in towns and on trails.

2. Assuming that rockslides haven’t closed trails, as happened in 2022, five days is plenty. Depending on how fast you hike, and whether you venture on any trails other than the main one that connects the five villages, or do something other than hiking, 3 days and 3 nights could be sufficient.

3. On both of our visits to the C.T., we stayed in Riomaggiore, the farthest south, and I’d go there.

4. La Spezia is where the cruise ships unload their passengers. We drove through it in 2022, and it was big enough that it didn’t seem to be swarmed with pedestrians. Didn’t stop there, though, so I can’t offer a detailed report of what it was like three years ago.

Check into the local information about hiking. The path between several villages is really just a walk rather than anything that would be considered "hiking". If you are really into hiking you should look into the "High Path" trail that runs along the spine of the mountains well above the villages themselves.

https://www.incinqueterre.com/en/trail-number1-high
https://www.cinqueterre.eu.com/en/footpaths-cinqueterre

If you're headed there for serious multi-day hiking you're likely to be disappointed in the challenge level of the area.

La Spezia is a work-a-day Italian town. You can catch the ferry to CT towns from there but it is not an exciting destination for tourists but a functional one. To experience CT stay in the villages and then you can at least experience them before and after the day trippers and get some sense of calm.

As others have said it will continue to be busy in September.

Have a great trip,
=Tod

We stayed in La Spezia last summer as our HQ for seeing the CT villages. Much preferred La Spezia to the villages, honestly, though to be fair ocean and railway conditions limited us to only setting foot in Monterosso. Be aware that the infrastructure hasn't kept up with the volume of tourists, so train travel and the hiking trails can be sporadic in their availability. And heavy seas, which happen often, can prevent the ferry serving the villages from docking.

La Spezia gets depreciated a lot here, but we found both the old town and the marina to be extremely enjoyable. Great place to see (and buy, for the superrich) megayachts. And the food we had in La Spezia was unsurpassed anywhere else we visited in our month in Italy. We didn't go anywhere near the cruise ship docks.

You can see the cruise schedule for La Spezia here, I would guess most of the people on these ships will be visiting the CT: https://www.cruisetimetables.com/laspeziaitalyschedule-sep2025.html

You can also check Livorno's schedule, but that port should have fewer people visiting CT: https://www.cruisetimetables.com/livornoflorencepisaitalyschedule-sep2025.html

I've only been one time - it was early September and it was a mob scene. Although it is very beautiful, I have no desire to return.

Five days/six nights is a LONG time to spend there, you really don't need to stay in each of the villages, you can cover them all in a couple of days. And I'm not even sure about staying IN the villages, we stayed in a hilltop inn near Manarola which involved taking a rickety bus up and down the hill - it was fine (beautiful views and a nice place to stay) - but I wouldn't have wanted to pack it up and do it all over again each night.

1. Yes
2. I think you can do them all in one day, if you can hike the whole day. I think it takes no more than 8-9 hours from Riomaggiore to Monterosso. But I would concentrate on the two best Monterosso > Vernazza > Corniglia. The shortest (Via dell'Amore) must be walked in the direction Riomaggiore > Manarola.
3. Choose one location only. Most prefer to stay in one of the 5 small villages, but others may prefer the bigger city of La Spezia. I never liked La Spezia much (it's a larger industrial and military port town), but some do prefer it to staying to the Cinque Terre.
4. Yes. Cruise ships dock at La Spezia. You can check the cruises' schedule for the days you are there. But obviously early September is peak summer season.

Listen to Stella B. We stayed 3 nights recently in Corniglia village. Unless you hike a lot, there isn't that much to do except eat. You can visit and explore the villages in two days easy on the train (buy the daily pass for the train) or hiking. Most of the villages look similar. We had time to take the train to Pisa and back in 5 or 6 hours on the third day.

We do not like busy destinations, and this is definitely a busy one. We have no desire go again; there are much better places (in our opinion only of course).

We spent three full days, and four nights last month and for us, this was perfect. Anything longer would be too much for many people. We based ourselves in Monterosso but you could do it in any of the towns. We visited all five villages comfortably (time-wise), took a pesto-making class in Manarola, had some time for the beach in Monterosso, and hiked between three of the towns (Corniglia to Vernazza to Monterosso). It was beautiful and relaxing and didn't seem so crowded after what we experienced in Venice and Florence. But we wouldn't have wanted to stay longer. As noted above, La Spezia is a work-a-day town, not as scenic as the five Cinque Terre towns (but maybe less crowded?).

Le Cinque Terre are busy all the way up to late November.