Gordstar,
I have a few hundred hours in the Airvan (so no expert!) and i have also done aerial photo ops. The Airvan is a pretty versatile aircraft for cargo and scenic flights, but i found it a little touchy in turbulence. Also it was mentioned in the thread that there is no rudder trim... I would consider that to be a major hassle if you are using it for Aerial photo ops, as the aircraft really should be trimmed out in all axis to make flying straight and accurate runs easier to achieve.
It is also not a very quick acft, so if you are going to have to ferry it across the state/country to get to jobs, it will be costly in both $$ and time. You do see a few C210's cuising around that have been kitted for aerial photo ops, so maybe that it a better option to look at.
If you do decide on an Airvan tho, my trick for getting comfortable was to stick an ERSA behind my lower back.. For me that seemed to give good support and worked as a good way to free up space in the rather cramped cockpit
All the best