I’m using the APU2C4 from the beginning and back teham Fulvio had to adjust the loader for it.
but all new versions work great.
Best is using an mSata SSD disk I have some of 16Gb and those are plenty of space to work with.
You can use SD but those cards breakdown much faster than the mSATA and are not so reliable.
the Temp of 30C is not an issue you have to be sure to mound the heatsink correct in the case for the cpu.
I use the english version so can’t say about localization.
The APU2 is powerfull and can handle 50 Mbit easy. but if you do special things like filtering firewall rules that could use cpu but I don’t think you will notice the impact of it.
I’m not using the captive portal and if i read your msg why would you use it 😉