2X2 will work for silkies. Where it gets cold, one needs more like 3 or 4 inch wide boards so they can cover their toes. Chickens aren't really perching birds like robins and sparrows so round rods aren't the best thing.
I use a sheet of plywood that completely blocks access till they are at POL. When you hear the egg song, that will be too late. Access to the nest boxes should be by the 17th week. They like to inspect and try them out for size for a while before they lay. If they don't get a chance to do that, it may be difficult to get them to lay there. Just block them in the afternoon before roost time.
Where to put food and water depends on your situation. I like to keep food inside so they can eat when they awaken if I can't get them out and it prevents wild birds and rodents. Water is another story. I have nipple waterers in most of the coops but anything open like a fount, I like to keep outside, especially in winter to limit humidity.