Hello, @LeonardoBR
Welcome to community. 
no. Don´t need to have a up to date care plan… just buy SFC.
This url, maybe help you…
No… Don´t need an extra license to use smoothing… just enable it, at speedfusion configuration.
yes… all peplink devices, have support to smoothing.
Yes… You can use domain rules or you can use IC2 (Incontrol).
Yes… You can use eSim… but need to use the IC2 interface to add an eSim profile to your device.
Yes… It is possible to use the WiFi of the device acting as WiFi WAN and WiFi AP.