What you are looking to get right now is both lower and higher demand. Look at the general search volume for the term. You should have a good mix of 100–500 per month and 1,000–5,000 per month related searches with which to begin your site (only do with less than this if you can afford to make fewer sales; if you make $1,000 per sale then you can live very well off of a 5 per cent conversion rate on 500 people).