I'd agree with consulting the CAA as the first port of call.
Also bear in mind that, at the moment, Things Are Changing
. Regarding the definition of crew/passenger, it has always been woolly. And if I'm honest, I think the CAA knew that too and on occasional were ambiguous or even contradictory. However EASA is taking over and generally, aerial work doesn't look like it will be afforded the same level of wooly-ness as perhaps it has in the past - at least not at the moment.
So crew might be those required by aircraft certification only (i.e. just you), or include "flight attendants, examiners and those authorised to conduct tests" which was another one I heard, or anybody except fare-paying punters. Which way is the wind blowing today?
I fly survey for a client across Europe. In the past it's always been Aerial Work. Now, they're looking at whether they need to use an operator with an AOC simply because they're missing out on winning work due to our lack of one. National Authorities are increasingly asking for one before issuing survey permits, even though in the past it was considered 'too much' and not necessary.
The CAA published a document in 2005 called "Summary of the Meaning of Public Transport & Aerial Work". It may help, it may not. Going forward under EASA, it may become irrelevant. Click here.
As for low-level stuff, I agree with Bayete. Use the CANP procedures if applicable. Consider putting two pairs of eyes in the front seats if your own lookout with be compromised (eyes-in/eyes-down guidance systems, for example). Even at low-speeds, it can be startling how quickly you can end up in someone else's face if you're not giving the outside world the correct attention. Trust me; been there, done that.
If you're hiring an aircraft, I'd make sure it was on a Public CofA at a minimum (or whatever the new EASA equivalent of that is), to cover one's backside.
HTH - good luck.