If you've got bell drinkers, just hang a five gallon drum off of the release pen and run 5mm pipe from the bottom, up around the handle a couple of times then down to the drinkers. Syphon the water through and they work a treat.
I personally like 20x20 release pens with a partition and 100 birds each side. I then leave them all in about five days then block release one whole side. I then let the remaining birds have the whole pen for another five days before block releasing the rest. Alternatively for greater numbers but without further pens, you can leave the partition intact and alternate every couple of days- one lot in, one lot out.
I like big plump 12 week old poults- you should struggle to get your hand around them.
Biggest key to holding them is un disturbed roosting. They're quite happy out in the middle of a tightly rolled field of winter wheat on what looks like a Tarmac car park but only if disturbance is minimal.
if you've got stubble, get a cultivator or sub-soiler up the tramlines to give them some broken ground to hide in.
if you've got maize, pay careful attention to weed control and try and get it bare as can be under the canopy as its the umbrella effect they like.
Some people like to keep them on pellets for almost the whole season but I think they grow stale of them once they start foraging for themselves and I like to get some 'tailings' 'cracked' or 'cut wheat' (depending on what your farmer calls it) as they go mad for it.
I dislike tin shelters despite the obvious advantages for dusting as it concentrates birds into a tight area creating a disease risk and also a pinch-point for sparrow hawk attacks.
If they're not strong enough to spend a torrential night in a maize plot then either your poults or your maize aren't quite ready