I would start at 1% with both. Some may say .5%. The Koolada gives a cooling mouth feel without being minty or menthol tasting.
I use 2% of both in a recipe I enjoy and vape all day everyday since Feb of 2015. I was an almost 40 yr Salem smoker and the 2% for me is not too much. I have tasted B&M menthol juices that tasted like Vicks Vapor Rub!!
The first vape
shop that I started
vaping with had 4 menthols to choose from ( actually # 10,20,30 and 40 ) and the last one took my breath away.................Vicks all the way! LOL
I am guessing at this point as I chose #20 and my friend chose #10 ( she smoked a lighter menthol cig) that those # may have been 1%,2%,3% and 4%.
Good luck, start low and work your way up.