You can disable ALL startups except the AV and those that you put yourself or need (e.g. sidebar). Disabled startups does not mean that those programs will not run when needed. It may just take a few more milliseconds to get them started.
If you are not sure, post a list of your startups. For that, this program
(startup button) is useful because you can resize the window to show all startups (unlike the msconfig window). The program has other nifty features too and helps with system security.