I am in Texas but my soil was similar to yours (clay). I added plenty of compost (50%), added 3-4" of mulch and made sure they got afternoon sun. Because my soil is more alkaline, I have to amend the soil when the leaves look chlorotic but that is rare (2 times in the last 8-10 years). My camellias tend to be very forgiving in that area. As a habit, I try to amend/acidify the soil in Spring (you need to ck your soil pH with one of those cheap soil pH kits and amend if necessary).

There is a Hawaii Forum where you can ask more information if you want; see the link below.

Luis

Here is a link that might be useful: Camellias in Hawaii

Camellia sinensis is a camellia, but very different from the other species. It likes acid soil, sunlight, and adequate moisture but very well drained soil. Zone 10 should not be a problem. There are ways to improve soil acidity, citric acid is one way, but naturally using oak or other leaves or bark to amend the soil. Peat moss can also add acidity, but be careful using this as it can also provide way to much moisture holding qualities. Check out the link below for a new company in Mississippi who are getting tea plants established in a field. They have some of the same issues.

Here is a link that might be useful: Great Mississippi Tea Company