After this question I will move future questions to your build thread.
Yes the machine is usable enough. What are your thoughts on using 3/4" MDF for the Z sides, top and back plate? I only ask because I have it laying around.
I didn't understand what you were trying to say about the outriggers. I did understand about using the aluminum bar stock, but not the parts about steel flat bar or steel angle. I think you meant steel cut at angle would be best, if so thickness? No worries, I'll be tackling the Z issues first. The reason I'm so hung up about the Z is that the top plate is already starting to crack and split, need to get what use out of it while I can.
Can you remember how many times you've had to tear your machine down as you upgraded?