The Scottish half term is earlier than the English one, the kids up here should be back at school by then.
I'm not sure how much difference half term would make. I have heard it said that there are fewer hikers because people with children are doing family things and people without are avoiding school holidays. If you are relying on B&Bs some of them might be busier, but some shut for the winter after the Scottish holidays - and that seems to apply to some of the hostels as well, at least during the week.
I would think it would be a nice time to do it, the midges are gone, and the woods up Loch Lomondside would be lovely.