That baseboard will bounce and sound like a drum!! That is unless there are lorts of supports underneath it, but I can't see any bolt holes apart from the ones down the outside? Why have you put the rails below the base, all the swarf will drop onto them! How are you going to mount the ballscrews and stepper motors? You're not doing a simgle ballscrew for the X axis are you? What is the gantry going to look like?

Have you looked at the build threads? Most (I do realise that you don't have to go along the same lines as most other people...however there is normally a reason why most of the builds look pretty much the same!!) look like mine below...

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