The most profitable thing to do is to run single type of flowers with best profits.
Dont go for full sets of flowers... If you do want to get full sets anyway, simply run the most profitable ones and sell some to buy all the others you are missing.
If you want to sell a large amount of a single type of flowers, check frequently a couple of days ahead and get a good sense of its actual value so you don't sell too low when ppl are competing to sell. You can always change the price when its high, but when sell low its gone and regretful.