Carpentry – Reason for Two Studs Inside Wall: Is It Safe to Drill Through?

Well, if it was an addition then the plywood was the old exterior sheathing. There would have been no reason to remove it. It is absolutely typical to leave it in place.

If you are simply putting a new receptacle back to back I am not sure why you think you need to remove wall material to go through studs. If you are implying that you need to go laterally along the wall to get to the new box location than NO, the cable CANNOT go along the surface, or even just below the drywall. You will in that case need to cut a channel in the wall to drill and cross studs. This can be done from either side if you don't want to mess with the plywood.

If you have the wire already through a hole you just need to cut a box into the drywall/plywood. A jig saw, RotoZip, MultiMaster, etc, will do a fine job of making the hole for the box.

You need a generator inlet that feeds a single outlet.(you seem to know what an inlet is, but it doesn’t need to feed the breaker box, it could just feed a single outlet.) This new outlet should be placed next to your current sump pump outlet, and properly labeled to avoid future confusion. (Assume here I’m talking about a future homeowner or tradesman— you won’t be confused but others might be in 10-20 years.) This new outlet would be dead when not fed by the generator.

Do NOT run your generator in the garage, it must be outdoors! Generators emit Carbon Monoxide which is odorless and extremely lethal.

(Note: the linked example is weatherproof, non-weather proof models are made for standard knockout sizes the are found on Hoffman-style enclosures, which are typically larger than needed for this project. Since the easiest to install are all weatherproof there is a message there—these should be indoors or in the garage.)