Looks good so far. Good job with the standoffs! Now use a hole saw to cut a 1" to 1-1/4" diameter hole in the center of the firewall for odds and ends to pass through. Don't worry, you won't weaken a thing. Next, thin out some epoxy with alcohol and paint the inside and outside of the firewall to seal it and perhaps stiffen things up just a tad more.

The only item that could trouble me are the nylon lock nuts. Nylon loosens with the application of heat. Better, IMO, are standard nuts and lock washers along with the use of Locktite. Better still is safety wiring, but that's not practical at this size.

Carefully think out your throttle linkage installation before you cut any holes. Be sure to allow for any radial movement as the throttle lever travels through the arc. You don't want to cut a bigger one than you need.

Pat