Giraffes aside I think being able to keep the livestock and animals apart is a good idea. Not just to rest pasture, but possibly to isolate animals at different times, to keep males from females, sick animals away, there are lots of reasons. Fencing isn't too expensive if you use electric and you can do up "zones" that can be opened, combined, closed etc. There are even temporary electric fence setups that are effective and portable. Is there a way to run water from the pond so you can service the other stock tanks instead of using city water?
I suspect that people might want nicely mowed and tended, poop free areas for events so you might find to get top dollar for your facility it might be worth it to isolate an area in the most scenic spot. As for insurance, just get lots and lots. Most of the petting zoo operations around here are shut down now due to the high insurance cost so it's definitely and issue. At the same time they will want to see the cool animals, I'd love to see springboks etc.
Regarding access, if you don't isolate the area, I think a cattle guard would be way easier than gates. Gates are just asking to be left open for sure.
I think you need to build another lake Eddie!!!