This is totally up to you! There's no right or wrong way to do it.
I prefer fewer ingredients so that I know the flavor will come out best. However, there's another way of thinking in that the more variety, the more nutrients you can consume in one sitting.
I also like to keep it to about 1/4 cup total of "boosts" so I don't get carried away and end up drinking a highly caloric Blast.
I know that's not much direction, but there's really no answer to your Q...
Check out some of our recipes here on NutriLiving to give you some ideas, then experiment. Maybe one day try 4 ingredients in your Blast, another try 7, then see how many you can fit in your cup without going over the max line. Variety is the spice of life :)