Another thing to bear in mind is that you're going to need at least two further tracks for your ambient mics - to neglect these will, at best, leave you with a rather sterile recording and, most likely, lead to you missing some instruments entirely.
Plus there'll almost certainly be occasions when you'll max out the desk's 16 channels and the needs of the room sound will not necessarily correspond to those of a decent recording... Something cheap and dirty like an ADA8000 feeding the HD24's third ADAT input would be an easy solution here.
I'd also think about getting some mics or their mount permanently installed in the venue so you're not stuck putting your mics in a suboptimal position.