I'm curious why you said to mill the 2X stock as soon as you got it home, or it would warp badly and you wouldn't be able to use it? I've always let my stock acclimate to my shop for a couple weeks, and then surface it to size. Of course, I was rarely using 2X construction stock, and rather mostly 4/4 hardwoods.
I thought screwing into the legs with a lag screw could have been done differently. Even with the oak plugs you put in, I'd be worrying about the legs loosening up over time with all the racking forces the table will experience. I think another way to have approached it would be to use 3/8 or 1/2 carriage bolts with a washer, lock washer, and nut. You could couterbore the head of the carriage bolt, and then plug the exposed recess on the exterior of the legs with a plug turned on a lathe, or purchased if an available one suits you. This plug could be removable, and slightly domed and proud of the leg surface. It could even be a contrasting wood color. You can probably still do something like this if the current design ends up giving you problems. You can also do the same thing but use a socket head cap screw instead of a carriage bolt. This will allow you to get an allen key on the head, ensuring that the bolt would never spin as you are tighteing it.