Sofa recliner difficult to lock in place

If you're working with leftover materials, you can surely pull 12/2 nonmetallic sheathed cable through conduit. You'll want to avoid lots of bends and long runs, as it will make pulling the cable more difficult.

If you're up for buying some wire, you might find it easier to pull single conductors through the conduit. Stranded wire is often easier to pull through conduit, though you might find it more difficult to terminate at devices. You could pick up a 25' roll of #12 THHN stranded copper, for about $8.00. You'll want 3, one black (ungrounded "hot"), one white (grounded "neutral"), and one green (grounding).

Since you're using a 15 ampere cord to supply power, you can use 14 gauge wiring instead of 12. If you're buying new wire, this could save you some money. If you're using materials you already have on hand, there's no problem using larger gauge wire than what's required.

Installing UL listed power strips is a safer bet. If you know what you're doing, there's nothing wrong with a custom solution.

You're cutting a mortise. The classic method is to drill a succession of overlapping holes, using a bit that's approximately the width of your desired mortise. You then clean it up/square it up with a (SHARP!) wood chisel.

Youtube it and you can see it being done.

I would advise you one small thing: I wouldn't run a mortise and tenon joint through the middle of a hollow leg. I'd fill the hollow part with wood, at least at the point that the tenon will penetrate.