Cedar Raised Beds

Will cedar walls on a raised bed garden effect the soil ph level enough if the bed were the standard 4' x 8'?

You should be fine. It is unlikely the effect ph by much if any.

in my experience cedar will last longer than just about any other wood (in Mich anyway)..we have some old cedar posts that have been in the ground for 50 years that aren't rottnig yet..high water table