You will flash the kernel as you normally would through recovery. In the thread associated with the kernel he also supplies a few scripts that can also be flashed from recovery.
Each script lowers voltage by a certain amount. Start with the lowest reduction script first and then test for...
I recently made the exact same switch. I can't really speak about the stock HTC Sense experience because I put Cyanogen 7 on it pretty much immediately. I've been extremely happy up to this point.
If you do make the jump to Cyanogen I would recommend pairing it with the LorDmodHD V4.5...
I was able to preorder around 10:30 central time this morning. The AT&T store in my "smallish" town, just south of Nasville, had a 3 hour wait. Glad I got in before the servers really went south.