If you use menthol concentrates, be aware that most are extremely strong. The same applies to crystals dissolved in PG. Most tobacco concentrates from Perfumers Apprentice and Flavour Arts are also strong. You might end up with a mix of 2.5% of each. I have diluted menthol concentrate in PG before dripping it into a 10ml bottle - because it is so strong - same with tobacco. A good start might be M-Type or RY4 tobacco and something like Flavour Arts Menthol (Arctic). I wouldn't start with crystals at first - I'd move on to that when you've made a flavour 'She Who Must Be Obeyed' likes. There are reviews of M-Type and the RY4 flavours in the Flavour Concentrate Reviews section of the site. Liberty Flights has a broad selection and you can pick up a discount code on this site too.