On the broadband settings not much to do here... I left it as is. For some reason it puts VPI / VCI numbers in, not required for UK but leave as auto detect will put them back again!
Split WiFi bands, put 2.4Ghz onto Ch 13, 5Ghz onto Ch 100, Security is set to WPA2+WPA3. Rename 5Ghz Ch, I just put 5G on the end..
Other bits you should look at is placing the box in stealth mode so no leaking data to outside world.
Blocking Port25 is good but needs to be tested!!! Depends on settings of email server your collecting from.