Body ideally with autofocus, as although primary usage will be landscape, I also want it for portraiture and possibly (shudder) weddings
Lenses I'd initially be wanting a 50mm and I'll be after a 110mm
digital back, at least 39m to start with, and upgrade in the future if my work takes off (I realise this is where all the investment is)
that's why I was thinking an H1 or H2 or H3, so I can keep the lenses/body and go bigger on the back if needed later on.
You are saying that you want an AF MF camera, at least 39 mpix, and a 50mm lens. I checked for you on eBay Europe.
An H1 costs about 700-800€ with viewfinder.
The H2 is hard to find and has no advantage over the H1 for you.
The H3 accepts film backs, but will not necessarily accept Phase One backs (I have seen one refuse third party digital backs, I am not entirely sure they were from Phase One). But if you ever intend to buy an IQ380, an H1 is 700-800€, so I don't see the problem.
The H3 backs were built with 22, 31 and 39 mpix. You won't find a higher resolution. So basically, you want an H3D-39. There are 3 on ebay as we speak between 3000 and 3800€ (buy-in, not auction). The H3D works very well, has the advantage that it accepts film back and the inconvenient that its rear screen is a disgrace. That's about it.
An HC50 lens costs about 1500-1800€. It is not as good as the version II, but you won't see much difference at the apertures used for landscape. Still, if I were you I would be an HC35 lens instead (about same price).
So, to sum it up, we are talking about a budget of 5000€ for what you want on eBay Europe. Even with shipping and taxes, we are still under your budget. What is the problem?