In very basic terms, and why you want to do them:

Attack surface is the ports and services you are exposing to the internet. Keep this as small as possible to reduce the ways your setup can be attacked.

Network topology is the layout of your home network. Do you have multiple vlans/subnets, firewalls that restrict traffic between internal networks, a DMZ is probably a simple enough approach that is available on some home grade routers. This is so if your server gets breached it minimises the amount of damage that can be done to other devices in the network.