Glad you decided to join the fun. An edge guide is good for a dado, but for a rabbet, I would use a straight edge clamped to the long end, spaced so when the router's base rides against the straight edge, the bit bites into the ply exactly the width of the desired Rabbet. You can use a straight bit for this, but a 3/4 inch long mortising bit cuts a beautiful flat bottom. I'd do this in several passes, with the last one only shaving a slight bit of material for the best possible glue up finish.
With ply, the end grain really sops up the glue, so put two coats of glue on the end grain so it really fills all the nooks and crannies.
When you do this, mark the edge of the router that will ride against your straightedge. Otherwise you could rotate the router and have an uneven cut and a nasty surprise at glue up.
Here's a diagram of a bit with bearings showing the difference between top and bottom bearings, something that occasionally confuses me.
The more I do, the less I accomplish.
Last edited by DesertRatTom; 04-23-2020 at 03:46 PM.