with unifi, it's not all or none. I started just with the AP's. Then added a PoE switch to run my AP's and UniFi cameras. Next I needed more ports so I grabbed another UniFi switch. Then I grabbed the USG4Pro to replace my pfSense (still run it in a VM for VPN duties. I just use the USG for routing/firewall/dns/dhcp/DPI) Lastly to round out my all UniFi network, I grabbed the UniFi 16 port 10GbE switch.... so I got bit by the bug and replace my other gear (Linksys APs, Dell L2/L3 switch, Cisco L2/L3 switch)
Good Luck!