Before a hen even starts to lay she builds up excess fat in her body. I've butchered enough pullets, hens, cockerels, and roosters to see the difference in fat. The difference is remarkable. This excess fat is what a broody hen mostly lives off of so she can take care of her eggs instead of being out looking for food.
I've had a broody hen leave her nest twice a day for over an hour each time to eat, drink, poop, and maybe take a dust bath. I had a hen that came off of her nest once a day every morning for fifteen minutes. That was the only time I saw her off of the nest. I never did see some broody hens come off of their nest but I knew thy did because they were not pooping in the nest. Nature has set broody hens up to be successful, you don't need to provide food or water near the nest or take them off the nest.
You never know how many eggs will hatch so I'd want to set at least four. It is easier on the chicks growing up if they have a companion their age, especially after the hen weans them and leaves them on their own. With winter coming I'd not want to hatch too many, the hen needs to be able to cover them all in the cold weather and they grow fast. Also your silkie is probably a bantam and Araucana are larger.
If you hatch you never know how many will be boys. You need a plan to deal with them. It sounds like that could be really stressful for you.
I don't know if you have this option in Wales. especially this time of the year, but if you could find some sexed day old pullets in two to three weeks she would probably adopt them. They need to be really young, hopefully not more than three days old at the most. I anticipate that could be a real challenge for you, it probably would be for most of us.
Personally I think you would be better off breaking her from being broody and waiting until next year when the weather will be nicer and you may be able to get day old female chicks for her to raise. The chances of her going broody next year are really high.
