How do you add multiple effects to the same clip

Do you want this for a whole movie or a single shot? Either way I think the simplest way is to export the project or the clip. Go to Share>Export using QuickTime. In Options click on Filters and select Film Noise in Special Effects. There are a lot of parameters including a sepia setting.

Normally you can apply only one video effect at a time. But for Sepia, black and white, and others that can be done through the video Adjustments tab, you are in luck.

Aged Movie should already have a bit of a sepia tone.

If you want more of a sepia tone or you want to fine tune the sepia effect you can do it with the Clip Inspector/Video Adjustments tab.

Note: Thanks to Jeff Carlson of MacWorld for this tip.

If you're looking for a washed-out sepia appearance, first open iMovie's preferences and turn on the Show Advanced Tools option, which adds more controls to the Video Adjustments HUD and other areas of the program. Select the clip you want to alter and press the V key. Set Saturation to 0 percent, and then drag the Red Gain slider to 143 percent, the Green Gain slider to 90 percent, and the Blue Gain slider to 53 percent (feel free to tweak these settings to customize the results). Click on Done when you're finished. Note that the clip thumbnail still appears in color, as the video was shot, but the preview reflects your changes.--JC

If you need to apply the same settings to all clips, first select the clip you have adjusted. Then Edit/Copy. Then Edit/Select All. Then Edit/Paste Adjustments.

Nice one. Lots more control this way.