Camellia japonica has the most hedgelike (dense and erect together in one plant) habit of the common ones, although even this varies with the particular cultivar being considered. There is a C. japonica hedge near an arterial in Seattle that is quite pleasing - except when its spent flowers are present. The mess these make (in this planting and elsewhere) is quite remarkable, if you have ever tried to clean up after one of these shrubs it is almost amazing.

4 feet is pretty short for a camellia, if you don't want a compact and narrow (boxlike) effect then one of the comparatively shorter, more willowy and spreading kinds could be used instead - especially if there is room for it to go sideways. Or put up a fence and train some willowy forms of C. sasanqua through it. These are more elegant and far less messy than C. japonica.

Get a longer season by interplanting various cultivars. Weather permitting, bloom could be had autumn through spring by including enough different kinds. Summer color could be gotten by planting hardy fuchsias (overwintered with mulching), unless these do not tolerate your summers there. These look great in front of camellia foliage.

Abelias look good with fuchsias, so if fuchsias won't work for you or if you want something additional these should also be checked out - although I don't think abelias look nearly as natural with Camellia japonica, being bronzy green sun loving shrubs. They certainly would go with bronzy green sun loving C. sasanqua.

Bboy, Thank you. C. sasanqua sounds good. I want a more relaxing and informal looking hedge. I plan to yank out those boring boxwood hedge with some dead bushes in between  look like missing teeth! I will also look into the companion plants you mentioned.