Own subnet contaning LAN port an own SSID


I’m new to openwrt. I bought a Fritzbox 4040 and flashed the latest OpenWRT image.
I have to connect the OpenWRT router to another Fritzbox / Router from my provider, which I can’t replace, because of telephony and so on.
I want to create a subnet, containing one LAN port and an own SSID, with an own DHCP range. The connection to the internet should be controlled by adblocker, whitelist and things like this (parental control). And a connection to some devices (printer, NAS) in the LAN of provider router should also be possible.
I think OpenWRT cann fullfill everything, but I need some tips or help at the beginning.


The first step is to change the switch configuration and move one port to an unused vlan.