S-Video also doesn't do well for longer runs. 50' may be pushing it. Composite, on the other hand, can run for a much longer time before you need to add a distribution amp in the line.
Once you go full HD and run everything HDMI, you probably won't need the compenent cables. However, if you find some cheap enough though (www.monoprice.com will have them cheap) they're good to have just in case you add some equipment that doesn't support HDMI.
Batutta also brings up a good point. If you get a receiver that ouputs HDMI and converts all other incoming signals to HDMI it makes hookups and adding equipment a lot easier. 1 HDMI from the receiver to the projector and everything else just runs to the receiver. So you could plug in composite, s-video, and component calbes into to the receiver and leave the other end tucked away, waiting for equipment to be added later.
Once you go full HD and run everything HDMI, you probably won't need the compenent cables. However, if you find some cheap enough though (www.monoprice.com will have them cheap) they're good to have just in case you add some equipment that doesn't support HDMI.
Batutta also brings up a good point. If you get a receiver that ouputs HDMI and converts all other incoming signals to HDMI it makes hookups and adding equipment a lot easier. 1 HDMI from the receiver to the projector and everything else just runs to the receiver. So you could plug in composite, s-video, and component calbes into to the receiver and leave the other end tucked away, waiting for equipment to be added later.