The problem about having food and water too close by when the hen is broody is that it enables her to stay on the nest and not get up to find food or drink. Then what happens is that she either gets very constipated or she messes the nest and eggs which can be an infection risk so I agree with your plan about getting them off the next once a day to go and feed, do their business and have a leg stretch.
My only two concerns are:
1. It's doubtful that you will get four hens going broody all at the same time - as has already been referred to and
2. What will happen when once the chicks are hatched? Will all the Mums be in the same area? because if they are - they are likely to fight and the chicks could come off worse.
Also - I can sort of understand needing to wait 30 days from order for day old chicks as it sounds like they would incubate a clutch to order for you….. but how come that translates into 30 days waiting for eggs - when the eggs are not going to need to be incubated for three weeks prior?
Maybe an option would be to get them to send you nine Sasso eggs once you have a broody that's sitting tight. That way you can time the eggs to the broody. It's still not a failsafe option. In my experience it only seems to work half the time but then - we have had accommodation problems this year which won't be repeated next year…. and we made the mistake of letting a broody sit on one egg whilst we were getting the hatching eggs that we wanted so when thy arrived - she only accepted one egg to sit on from the imported clutch - hence an emergency trip to Wynnstay one Sunday morning to purchase an incy.
This thread reminds me of the Dutch polder model of political decision making - keep talking and the solutions might slowly emerge