VPN on stock or custom?

I'm new to VPN, bought one for my friend's bday and thinking of buying PIA VPN for myself.
Instead of single device setup, I want to set it at the router level.
Can I set this up on stock?
Or do I need to flash custom FW?
If so, FW recommendations?

And is it easy to toggle between default and PIA?

I apologize for my ignorance.
I've had my N66 2 months now and love it.