Looking good. If you hadn't ordered your stuff yet you can get away with three linear slide blocks just fine, two on the top and one on bottom or visa versa. That is all Tormach used. Also, I found the extruded aluminum channel with aluminum rails molded in like Tormach but as cheap as my setup was I didn't figure it was worth going that route. It would save a few bolts and machine work though.
Also, I haven't had any issues with sag so I'm not using a the bottom brace going to the column. Your aluminum profile for the mount ought to be plenty stout as long as you make sure your bolts won't allow stuff to slide or come loose.
The weakest link in my entire setup is my triangle shape mount that mounts it all to the column and honestly that was due to me adding a 15# cover to the thing.