The usual way to make a liquid detergent more liquid is to add more water or a little ethanol. It will undoubtedly go off whether you cut it or not, and if there is no preservative in it already you will need to add some. My knowledge of the matter isn’t good enough to advise on what or how much though: I buy that sort of material ready-made when I need it.
On the fragrance side there are many, many complications involved with selling home-made fragrances and these are all explored extensively elsewhere on this forum. However the one thing that isn’t a problem is selling a fragrance containing ethanol - the vast majority of personal fragrance sold worldwide is in an ethanol base - why do you think you need to use something else in order to sell it? Unless you are using only a very small proportion of water (5% by weight roughly) your perfume will be cloudy (which also means it won’t keep well) unless you add some sort of solubiliser or co-solvent.