You can wire them all together like you said, that's what I would do. Sometimes I have seperate flowers on different length wires or I wire some together and some not as I'm decorating the cake. But remember then the back view of the cake. It would be messy back there unless you add flowers there as well or find another way to cover the wires up. You can also have some flowers not on wires and just dab a teeny bit of melted chocolate where you can't see it and avoid the wires in the back view completely.
Thanks for the advice. I think I will make my flowers and try out the arrangement on a dummy cake. There might just have to be a "back" to the cake. We'll see.