I think you would be fine with the normal USG. Where it gets tricky is the type of routing, traffic management and throttling you’re doing. If none, you’re fine with a USG, but if that is on the menu, Pro all the way! Hope this helps!
Maybe @LTS_Tom can give a better insight, but I just finished a house install of a 450 mbps connection for a house that will have around 6 to 20 clients, plus some other guests from time to time, and I did a 4 vlan, with 3 of them on wifi, with guest limitation on speed and has DPI enabled, and the USG is running fine, atleast so far.
If you don’t care about enabling QoS or IDS/IPS, then you can go with the USG.
If you want either of those, them you don’t want the USG or USGP - neither can do 1Gbit/s with hardware offloading disabled. Your only options at that point are the UDM or UDMP. Or wait 3-6 months for the UXGP.
Summary: The USG and USGP are old and right around the corner from being retired.