Leros, Kalymnos or Lesvos in mid October?
 

I'll be working in Greece and have a few extra days in mid October before I head back home. I'm looking at flights that work with my schedule and Kalymnos, Leros or Lesvos. work My goal is to visit an island I've never been to and I prefer the more off the beaten path places. All three island seem to fit the bill but, since it'll be mid October I want to make sure things will still be open. I don't need much, but don't want to feel completely alone. I'd love to be able to go hiking, maybe kayaking. Does anyone have experience with these at islands this time or year? Or just in general?

I have not been on those islands but Leros holds 8000 population, Kalymnos double that on double terrain, while Lesvos is much much larger ~1.630 km2 and holds nearly 85000 population. I doupt there will be much open infrustructure on the smaller islands, I know that Kalymnos still gets day tripers from Kos but I don't think many people overnight there on October. There are a couple of package holidays in specific areas of Lesvos running till early October I believe, but even if there is no visitor on sight, this is a lively working island, not depending solemny on tourism.

I've been in Lesvos off season and it was interesting; not really beachy, but interesting. Big wildlife island (esp birds)

I've been to all three but a while ago now.
Kalymnos and Leros in May 1987,Lesbos in May 1989. We travelled from Kalymnos to Leros by boat which is not very far.
At this stage my recollections are these. (We had young children with us each time.)
I believe that Kalymnos has a year-round population and so (if I'm right) it should not be all closed up in Winter. Poeple were very friendly (but that it true all over Greece) the honey on the yoghurt was wonderful! We took a trip over to Telendos which was a disgrace. The beach was littered with rubbish to include glass and rusty wire.My memory of the capital is of a live Greek town ( as opposed to a tourist resort.)
Leros was less accessible and had fewer tourists. The town on the hill-sorry names escape me was lovely. We walked quite a lot. There is /was a town there with lovely ice-cream parlours which had something to do with servicemen during the war. The island has/had many institutions for the mentally ill and at that time they were a major employer. It gave you cause for thought to see the designated buses taking employees to work every day whilst we enjoyed the weather and beaches. I remember seeing a rat in a restaurant garden- something which was far less common then than now.We took a day trip to Lipsi where we had to sit in a restaurant because the beach was impossible for us to return from with two tinies. My daughter was majorly spoilt in this restaurant.

Lesbos was far more tourist orientated. We stayed at Kalloni. I particularly liked Molyvos and Petra. Weather was quite windy in May which made it colder than expected.
We've not returned to any of these three although we have been back to Greece seven times since and are currently going every year.