Material advice and advice needed

Okay so after getting the parts to build my own cnc mill but not having the time too get it running i decided to try to use emachineshop.com.
So i got my part designed and got it down to a decent price.
It is mirror mount that uses 4 bolts to adjust the angle of the mirror for my laser projectors.
Now i have seen these made from aluminum before but the current ones on the market are made from brass, see pic below.
http://i755.photobucket.com/albums/x...oukan/flex.jpg
I was told by some that aluminum will be fine as it wont creep any noticeable distance from 60f/15C to around 90f/32c
How ever i have others who say it will and i should only use brass.
What do you guys think?

Also as far as design i made a 3d model that showed using more cuts to show all the features i wanted.
http://i755.photobucket.com/albums/x...opticmount.jpg
http://i755.photobucket.com/albums/x...xpriceside.jpg

And this is my cheaper design in their limited software using less views.
http://i755.photobucket.com/albums/x.../flexcheap.jpg
http://i755.photobucket.com/albums/x...xcheapside.jpg
The issue i am having is the chamfer of 3mm 45deg i selected to be on face where the mirror attaches does not shop up in the software.
I know its not going to due to its limited in nature.
So how do i know if it only put the chamfer on the left and right side?
Also in the back you will see the far edge is flat i have selected it to be round with a radius of 0.994mm
I know that might not be able to be reached due to the tool diameter and if its end or ball and that it might need some comments.
I am unsure how exactly to say the things in the right professional manner to make sure these come out right.

If you guys have any advice on anything hell maybe even another shop that would be great.
I like making things in inventor much better than that limited software.
Im looking to get over 100 of these made.