Hello Roberto
Replace router-1 and router-2 with only one firewall. This firewall should be capable to support vlan trunking (802.1q). Each of the required security-zones can be provided with individual vlans.
INTERNET------Internet-Router-----Firewall====do1q===switch
If you have questions let me know.
Regards
Daniel
Hello Roberto
Trunking means transmitting multiple vlans over one single link (cable).See attached file. In this scenario all vlans are protected by the firewall-rules. If you choose the appropriate hardware (firewall, manageable switch with PoE and WLAN Access-Point) with vlan and trunking support, you will own a scalable solution. Of course, this is not the cheapest solution, but it lets you sleep soundly. 
And yes, if you never configured on your own such a setup then you will need assistance.
Regards
Daniel
Yes many questions.
Perhaps you find some answers in my Thread here, written in German:
Netzwerk und Shelly - kleines Grundwissen für Einsteiger
Use simply the translation function of the browsers.
