Aluminum router build - Could use some input

[Tumblebeer]

I'm about to start a build of an all aluminum router. It's not my first build, but the previous ones were MDF abominations that should have been birthed squatting over a bucket of water. Let's not mention them again.

Right now I'm in a design phase, and I'm very open to input. My build is constrained by rather small space, complete lack of decent tools, severely lacking metalworking skills and a tight budget.
I've uploaded an album with some pictures of the build, and a few FEA simulations giving a hint of where the weak areas of the construction are.

http://imgur.com/a/F77V6#0
Edit: Revised build after getting some tips - http://imgur.com/a/pM3GU
Edit: Third iteration: http://imgur.com/a/kszzz
Edit: Fourth iteration: http://imgur.com/a/zyBVw



It's designed using 60x60 aluminum profiles and 20mm 5083 alu plates. I know 5083 is less than ideal, but it's what motedis.co.uk is carrying, which is where I plan to buy the bulk of the materials.
The linear parts are designed from a kit: http://www.aliexpress.com/item/3-SBR20-300-600-1000mm-set-3-ballscrews-RM1605-ballscrew-support-3-BK-BF12-3-couplers/522559269.html

My questions are:
Will I be severely crippled by using 5083 instead of 6061 or 6083? If so, do you have a recommendation of an alternative to motedis? Apart from that, I am very impressed by them, without actually having bought anything yet.
I'm considering going dual ballscrews on the x-axis. But I only have 3 steppers+drivers, meaning it would be a pretty hefty investment to get everything extra for that. Is it worth it? Is it essential for success?
I'm having some trouble finding a good way to mount the ballscrew supports, any ideas?
I'm going to use a 2.2kw water cooled spindle. Any ideas on a cheap, closed loop cooling system? Also, anyone tried the "Sanven" spindles on amazon.co.uk?

Apart from that, I'm looking for any and all input on how the design could be improved. I'd like this one to be near perfect before I start buying stuff.