To summarise then, you have some form of extremely fast internet connection - probably 2.5GbE synchronous?
And you want line speed to your wired devices and as much as you can get on your wireless devices and you like Unifi’s marketing?
Fair enough.
Then you want a UniFi Dream Machine (UDM) SE and that will take your 2.5GbE input into its 2.5GbE RJ45 or 10GbE SFP+ WAN port (you may need an RJ45 to SFP+ adapter depending on how your ONT is terminated).
You then link to your ‘hub’ switch - the UniFi USW-Enterprise 8 PoE is a 2,5GbE switch with PoE and an SFP+ uplink to the 10GbE LAN port on the UDM SE or you can go 10GbE with the USW-FLEX-XG that you already have (again, you’ll want an SFP+ adapter to link the UDM SE and the USW-FLEX-XG). So you now have a choice about your wireless LAN. If you go for anything other than the U6-Enterprise access point, you may as well keep your USW-FLEX-XG and power the access point off the UDM SE because they all have 1GbE links. If you go with the U6-Enterprise then you’ll need the USW-8-Enterprise switch and a SFP+ DAC cable.
Budget System
UDM SE
USW-FLEX-XG
SFP+ to RJ45 adapter to take the 10GbE LAN port on the UDM SE to a port on the USW-FLEX-XG
U6-Pro access point powered and connected direct to the UDM SE
That would give you wired 10GbE access for 3 clients and anything up to 900Mbps on WiFi.
Fastest WiFi system
UDM SE
USW-Enterprise 8 PoE
0.5M DAC to connect the UDM SE to the USW
U6-Enterprise access point powered from the USW-Enterprise 8 PoE
SFP+ to RJ45 adapter for the second SFP+ connector on the USW
That would give you 2.5GbE wired connections on up to 7 devices, a full 10GbE for 1 wired device and potentially over 2Gbps on a good quality WiFi6E client.
I would probably argue if you’re spending this much money, get the USW-Enterprise 24 PoE because it’s 3x the ports for another £200. But I am a salesman LOL!