What will your budget be after selling your nex7 kit?
A 85mm f2.8 pc-e would give you ample dof for your water drops.
Is the 85 a macro? The only macros I have come across are 50-60's and then 90/105. Part of the issue is minium focusing distance. I have a "macro" lens, but the MFD is something like 4 inches? So I end up with water drops all over the lens every time.
I probably have too tall of an order here. If I am lucky, I'll get about $700 for the setup. I want "what I have now" only in Nikon, for pretty close to an even trade. So I need 1) a way to do macro and get at least as good of results as I'm getting now 2) a longer lens and 3) a backup body (doesn't have to be fancy) just in case I need to send my main body in for any reason.
To check all three boxes, I am also considering a long lens with some extention tubes, or getting the long lens and then a teleconverter for my 28-105 "macro" lens so that I can get the MDF away from the drops....