You would definitely need some sort of cooling with a ferm that large or the temp will get away from you is what I have been reading. Also when the fermentation was done would you run it all in one day with 4 runs if so that would be a long day for sure. Having only one ferm would also limit you on the variety of products you could produce whereas having 2-4 gives you a lot of possibilities. Also you have to consider that something could happen to your fermenter that puts it out of commission for a few days or longer and if you only have one ferm, well you're shit out of and luck scrambling for a new one. Last but not least you just look more professional from a customer's standpoint who is taking a tour in my opinion.
I would get two 600 gals, solves most all the problems. keep in mind you cant fill the ferms to the brim (or the still for that matter) because of foaming. Anti-foams knock this down considerably but I am not sure to the extent, someone might be able to give us an answer here. I am also fairly sure if you're trying to achieve certain certifications like kosher antifoams might not be allowed.
I am starting off with a 1000L Still and
2x 2450L Stainless Jacketed CIP Ferms
1x 2000L Mashtank
Again I have no actual experience but I am just finishing up the research phase of this venture and am hoping to lend some help in exchange for all the help I received on this site.