Excellent improvements to increase regidity. Another thing you may wish to consider is adding additional idler wheels, as @dddman is doing here:- http://www.openbuilds.com/threads/openbuilds-ox-cnc-machine.134/page-75#post-13688 Giving more belt teeth in contact with the drive pulley will almost certainly give better performance and more than likely improve belt life. Just a thought. Tweakie.
Thank you Tweakie, I will add some idler wheel in my next order of openbuild component! I bought the spindle from ebay, it have no brand but its model number is HXKJ-GS52-400W. Operating voltage: 48V 10 A. Speed 4500-12000 rpm.