I've been through phases of monitoring network activity, and limiting outgoing connections - it is amazing how many apps fire off to the web at random times.
I used
GlassWire (free version) for a while - seemed pretty good, but I never discovered any 'hidden threats' just loads of apps checking for updates (which you can usually turn off in their settings).
I still use WinPatrol to monitor startup, even though it's no longer updated/supported (shame).
Ever since their major update a while back, you can get plenty of alerts from MalwareBytes' Real Time Protection mode.