As long as you test all the flavours separately and gauge the strength and wether you like this flavour from bla blah rather than from blah blah, blah or blah, you'll start to know the perfect one for each flavour for you from a lot of different manufacturers ..
After a while when you think this and that will be nice together your already know the exact concentrate you're going to use..
For instance if I want a good sharp green apple in a mix, I I like the Capella one.. A lot.. And to add a bit of strawberry, from experimentation I know I like Capella sweet Strawberry too.. And for kiwi.. I know of I like TFA Kiwi double.. And you know how strong each flavour is so you can near enough guess each recipe.
Once you know what you like it gets way easier. Although I keep getting fucked over by my taste changing so so often grr "but I loved it yesterday" often comes to mind for me.