3. How much of those small bottles of flavors you get from say Bull City do you need {approximately} ?
Your posts seem to indicate that once you get your new base mixed, that you're planning on trying to make the whole amount at once...or at least 1/2 of it...into the Strawberry Waterfelon you like. Otherwise, you wouldn't be needing larger bottles of flavorings. IMO, that's very risky.
Most people usually make only 10mL or 15mL of a new recipe at first...to see if they even like it. You can "tweak" those small amounts to get it to your liking...while noting the changes you make to get there. It may even involve trying different Strawberry and Watermelon flavorings in those sample mixes. Then...use the info. on the changes you made to the original recipe, to make larger batches when you want them.
If I misread or misunderstood what you posted though, I apologize.