Thanks Leigh. Digital projection is probably the way to go and if it weren't for the significant cost difference I probably wouldn't be considering analog. This project is set to screen every night for 22 nights so the costs add up!
I may be able to rig the slide projectors so that they are 10-15m from the screen. This makes a wide angle lens imperative. I was wondering if anyone could name a few lenses (that I might be able to find on ebay) or any 35mm or medium format projectors which come with a wide-ish standard lens.