I actually had my tank dilled at Red Coral here in Calgary, and they did a fantastic job quickly
. That being said I would do it myself next time. I based it off cost when I did mine, two holes were 40 bucks while buying a diamond encrusted hole saw was somewhere around $60-80. Cheapest I found was on eBay and im way to impatient to wait for shipping. As for the hole size that is going to depend on the bulkhead. And the bulkhead is going to depend on the size of your drains and returns. I just drilled for my drains which are 1 1/2 inch but Im not sure what diam hole that bulkhead would require. Ill see if I can dig it up somewhere on the net (EDIT: 1 1/2" bulkhead requires a 2 3/8" hole, found on reefland.com), Im sure many people on canreef would know as well.