That’s pretty much my setup you just described, though that was before the UDM-SE came into existence, I have USW-Pro-24 (for the 10Gbit SFP+ ports) as core switch, a USW-Aggregation for 10Gbit devices (homelab), and a USW-Enterprise-8-PoE for 2.5Gbit PoE for the U6-Enterprise.
There are 2 upsides to the SE:
- It has PoE, if you’re only running a single Gbit AP off it or a few cameras then you don’t have to get a PoE switch elsewhere.
- 2.5Gbit Ethernet is a kinda weird standard, and it doesn’t really exist officially in SPF+ form, so if you have coaxial Internet and your modem provides between 1Gbit and 2.5Gbit then it may be difficult to plug that into SFP+ WAN on a UDM-Pro unless you have a SFP+ RJ45 1/2.5/5/10Gbit module.
Sounds like you’re running fibre directly to the UDM-SE though, so your options here in Sweden will probably be 1Gbit or 10Gbit anyway, which are both easily supported using ISP provided SFP/SFP+ modules, I’m on Bahnhof 10Gbit personally. Worst case you can just keep using the ISP provided CPE and chuck a SFP+ RJ45 module in the WAN port.
I would wait for response from support before expending the effort to ship it back personally, but otherwise I’d probably do exactly what you describe, except with a Pro model switch for the 10Gbit SFP+.