3kW air-cooled spindle. Mainly decided on due to the K2 machine. I'm reluctant to use water-cooled as don't want the faff of pumps and water near my dried woods - after VFD control I'm also running out of capacity on the basic parallel port breakout board. I'm a bit worried about the noise - I use handheld routers a lot - I hope that an air-cooled spindle will be a lot more quiet - does anyone have any experience with one?
- For weight, I rely mainly on extrusions, using plates only where necessary. All plates are 15mm thickness. Machine size is kept as small as possible.
Air cooled spindles are generally very noisy. Not sure why you think the water cooled ones are going to put water all over the place as they are fed with 6mm tubing and the pump and water container can be anywhere off the machine. They are also quiet .

Re the plates I would use 20mm and if you don't want to machine it use cast as that will be flatter.

Have you checked out if any of the bolts clash with each other ie on the bearing blocks for Z and Y