If your using thick enough plate for the main structure braced correctly then you shouldn't need to mess around with epoxy etc. Esp if your mainly HSM as the cutting forces are much much lower.

I wouldn't use a Gas strut and would go with counter weigth down the column centre running along some cheap round rail. Every industrial machine I've ever seen use's this method inc £250,000 5 Axis machine I recently worked on.

I'm interestd to see the spinlde and motor your going to use can you post links to it.?