Is it possible in the current firmware?
Can it work without enabling cascading mode as well?
The idea would be to have external devices surfing the web have the IP of the router while local devices surfing the web have the IP of the VPN.
Would there be a big performance degradation from running VPN server and client services simultaneously compared to separately? Perhaps it depends on RAM of the router model?
If actual traffic is only generated on one or the other side, but not simultaneously, would it still be advisable to turn client and server on selectively when needed rather than keeping both on for convenience?