Definitely better to leave things disconnected if you’re not sure, since it’s a lot easier to connect them up again afterwards than to disentangle things which are already connected :)

One thing I find really useful for property boundaries is the OSMUK Cadastral Parcels layer. If you haven’t found it already, it’s under ‘Overlays’ in ‘Background Settings’ on the right.

Just message me if you have any questions about editing locally — happy to help out where I can. :)