Id definitely recommend PC lighting for ANY marine plants. I had 2x18w 50/50 bulbs over a 20g tank and the caulerpa would only survive on the upper reaches of the rockwork mere inches from the waters surface. I added another 2x18w 50/50 and the caulerpa thrived in the top half of the tank but would not grow in the bottom half of the tank, and it was only 18" deep. If you want to try caulerpa with your current lighting the hardiest species are definitely C. taxafolia, C. mexicana, and C. prolifera. Ive found C. racemosa absolutely thrives in higher light, but doesnt seem to tolerate lower lighting.
Halimeda and shaving brush need calcium and Ive found they really only thrive in a reef tank. I have no experience with sargassm but Id assume it needs higher light as its a floating plant. Id also assume the various kelps are similar.
Hope that helps a little.
Jon