Well fwiw, here is my $0.02.
It looks like you are using 1530 extrusions for you outside frame and it looks like you are spanning about 6'. I think this will flex more than you would like (I know it would be more than I would like). I would have made it more robust. Here is a link to automation4less. They have some great pdf files that will easily allow you to figure the amount of bending you can expect.
structural aluminum extrusions, TSLOTS, T-Slots, 80/20, Parker, Item, IPS, slotted extrusion
As far are autocad, I'm sure there are people who swear by it. I tried it once and found it awkward and hard to learn. You couldn't give it to me. I use TurboCAD. It's easy to learn (relatively) and cheap. It will probably do all you want and more.
Good luck.
Rick