requesting real life experience with 904 lock-up with manual switch

Amazon.

Basically the same relays you would use for an electric fan should work.

If the relay is single pole double through it will work for the NO and for the NC relay ( you need 2 separate relays. The push button switch can be any type of momentary NO momentary switch. ( It can be a push switch or a toggle switch your choice.

This relay should work for both relays.
Screenshot_20210803-203002.png
For a momentary switch, if it can handle 1A that should be enough.

As for the reallys only one of the relays needs to carry any current (unknown till you can measure the current draw by the lockup converter, then double it. If it draws 5 amps be sure your relay can handle at least 10 amps)

But for simplicity use the same relay for each.

For wires I would suspect that 18awg would be fine.

Be sure to fuse the 12v source