I would get GlassWire to monitor data usage (you need a copy on each computer that uses the network), and you definitely need an antivirus package (McAfee or others).
With regard to Glasswire, I just wanted to let you know that, if you do download and install it, you only need the free version. Many of us use Glasswire, as it's a great way to track what's using data on the computer it's installed on, and the free version is just fine for that. There's no need to purchase the "full" version. 🙂