Two simple routing question using the Firewall

Yes there is, check http://docs.nethserver.org/en/latest/firewall.html

Firewall policies allow inter-zone traffic accordingly to this schema:
GREEN -> BLUE -> ORANGE -> RED
Traffic is allowed from left to right, blocked from right to left.
You can create rules between zones to change default policies from Firewall rules page.

You can create as green as you want, I want to remind you that you should create VLAN only when you need to create two or more logically separated networks using a single interface