I want to splurge on something for my cake decorating.  I haven't started a home baking business yet,  but I'd like to. 

My three choices are:

1)  An airbrush kit

2)  An edible image printer 

3)  Cake boss software 

I'd like all three, but want the one that will "realistically " use the most and would be the most beneficial to me if I am able to start my own business.   

Which would be the best to start with?

since you say "if" you start a business I say go for the airbrush but if you were sure about the business thing i'd say go for the software

1 or 2! I already have an airbrush, but the edible printer is next on my list!

I think, as the others said, the airbrush would be the most useful   W/0 knowing or seeing your work it would help you the most 

I do not have a cake business, nor so I want one.  For my purposes, the airbrush is my preference.