How much% Cholesterol do I use as a w/o emulsifier?

1 to 2% should suffice.  

In Your composition I would replace the white Vaseline 10 g with liquid paraffin. This liquid paraffin should warm up to   +/-90 ° C. In this warm liquid paraffin, the cholesterol is dissolved. Solving the entire amount of cholesterol takes time because cholesterol is not so well soluble; So the cholesterol should be completely dissolved. After that, you can gradually add 90   g of White petroleum jelly and then the purified water that you have cooked in the preceding   and let it cool down to +/-60 ° C    . This should give you   a nice W/O emulsion type Eucerine Aqua.