Ask HN: Joint venture negotiation advice..?

Some context: I took the plunge and left my programming job last September to build something useful: a simple yet easy to customize web-application for the HR/recruitment market.

I recently demonstrated an early version (about 60% complete) to the founder/CEO and technical director of a well established HR consultancy that also provide bespoke recruitment software to large organizations. The meeting was very positive:

* It confirmed my application was doing the right things as far as HR people are concerned

* We "got" each other's outlook

* We had similar visions of how technology might shape HR/recruitment in the future

They recently got back to me and have proposed a joint venture based on my product: they pay me whilst I complete the product, I would retain ownership of the product so long as they have some sort of exclusivity in a revenue sharing deal.

This is a good opportunity: I'd get a route to market, a pool of HR expertise to draw from and an established partner.

However, I'm a software developer (among other things) and this is my first "venture". My biggest concern is my naivete so I'd like to ask the HN community for advice:

* I'll register a new company through which I'll do this work (rather than just being "that guy hacking away on stuff"). Any tips on how best to do/structure this? Or is it as easy as it looks (in the UK)?

* Exclusivity contract: I'm assuming it will be for version X of product Y in location L for duration D in market M. Currently, M=Govt/public sector/"third" sector and doesn't include the private sector. What should I expect for L and D and what else might one typically negotiate (I was thinking in terms of sales targets)?

* Revenue sharing: I'm (again) assuming we'll be negotiating on % of sale price. What are typical percentages for the split between software developer / reseller?

* Any legal gotchas I should know of / avoid?

* Anything else I might need to know when getting into a situation like this..?

My personal long term aim is serial entrepreneurship.

Thanks in advance... :-)