Hi again

I was looking at some of the extracts on BB and became intrigued to try a seaweed bar.
The seaweed extract says this .. Suggested usage rates: 3 - 5% in liquid soap, hair products, cremes, melt and pour and CP soap.
I will be starting with testing 4 oz of everything I try (one bar) so what would that be in ounces or ml? No gram scale yet, so no grams lol
I also saw a seaweed scrub recipe on the site, I assume that is used in the shower so you can rinse it off (I've never used a scrub before!)
There was no preservative in the recipe, but see that the extract has... Germaben II added at 1%
would that be enough or do I have to add more? Here is the recipe for the scrub
Seaweed Body Scrub
* 1 lb Sea Salt
* 4 oz. Sweet Almond Oil
* 1 oz. Melted Shea Butter
* 2 oz. Melt and Pour Soap Base
* 1 oz. Seaweed Extract
* 1 tsp. Fragrance
Melt shea butter, M&P Base along with Almond oil. Add to Salt. Add Extract and Fragrance mixing thoroughly.
Also how much can you add to MP before it becomes mushy, like additive wise. I also see some clay and salt I would like to use, just wondering if there was some formula of how much stuff you can add to a MP base.