I just found out someone who did what I want to do: http://forum.mikrotik.com/t/mikrotik-as-a-neutral-router-with-isp-router-movistar-hgu-in-bridge-mode/106089/1
Appart from my doubts in VLANs… Any recommendations in firewalling?
How do I connect to my ISP’s router if something wrong happens?
Do I need DNS cache?
Thank you!