Sorry I forgot to respond to your last bit.
October in Scotland can be very nice to hike in.
However, as I've already hinted at, October is the point at which the weather really begins to start turning towards winter so be aware of that, there can be lovely sunny days as well as cold, windy, wet days.
On the plus side it's out of the famed midge season so you'd be unlikely to be eaten alive
Hopefully some long distance walkers will reply to you to give a better idea of a suitable long distance walk for later months.