Thanks, Brendan. Absolutely agree with everything you've said.
1) We're definite about keeping the premises in our own names rather than the company's.
2) We've spent considerable time thrashing out every conceivable (and inconceivable) snag, change of plans, fall out and foul up (all the way from "What if I want out in a few years' time?" to "What if I didn't like the paint you chose.. and came at you with a knife?") and there'll be a ruthlessly iron clad legal agreement drawn up, signed only after each taking legal advice independently of the other. I've seen as little as a fiver cause issues between friends, so we'll be taking no chances!
We have sufficient capital to go 50/50 on the deposit and the business start-up costs, so we should be able to avoid the extra hassle of seeking a business loan on top of the mortgage.
Really, at the moment we're just a bit lost about where to start looking for the finance we need. Can we look at 'standard' mortgages for the whole property, or will we have to get a commercial mortgage? If so, can we somehow treat the property as two (in fact, where we're looking, the business premises is self-contained and could be treated as a separate entity), and get a residential mortgage on the apartments? I'd just like to have some sense of what the possibilities are before I go making enquiries of various lenders.