nicad - Colin!
I'd humbly suggest a look at the cooler kits from ARTX at
www.artxltd.com which use a vortex tube to provide below zero air from a regular compressed air supply. They are fanf**kingtastic for very little $ and you will achieve much better cooling for the same airflow. And yes I think internal housing cavity cooling is best, cuz that's as close to the source as you'll get. Smalley and others have online tables and calculators for the wave spring force. I know that several professional spindle makers use a closed loop cooling system, but if you're prepared to pay for a little air, the ARTX vortex cooler is s-o-o-o-o inexpensive. For casual use rather than 16 hours x 6 days a week, I think you're pointing in the right direction. SteveG and HuFlungDung have given you top tips on the bearings, too. Regards, Terrence