Integrate lan, wifi into network

how does the configuration needed to be for the following scenario

I have an existing 192.168.1x network
with a router

Router IP Gargoyle

WiFi is done by Fritzbox mesh devices

I want to integrate a Openwrt Router
So it is connecting only by WiFi into this
Fritzbox WiFi so I can connect from every computer to the Openwrt Router.

Additional on this Openwrt is a ddserver running
which is beeing connected by USB dslr

I want to use qdslr dashboard on computer and android to connect to the Openwrt

I am not sure
a) how the configuration needs to be
on Openwrt
b) is it bridging or wds I am looking for
or something else
c) if I need additional software for this task
d) I have devices with Openwrt 17 & 18
MR3040, WR902AC beeing used
e) can I just delete / deactivate firewall for usage in my lan or do I need it for successful connection in this scenario

Thank you in advance for your help.