Service Packs and Patches

I have several PCs which I am going to completely overhaul and do a clean installation of Windows 2000 Professional.

I almost feel dumb asking this but it has never really been explained to my satisfaction by anyone.

The software I have is Windows 2000 with Service Pack 2.

1. After installing this, do I need to install Service Pack 3 and then Service Pack 4 or can I go directly to Service Pack 4.

2. What about all of the miscellaneous Microsoft Security Patches? Are these included in the service packs? Or, do I need to go back and reveiw all of them and install any related to W2K Pro? How do I know where to begin?