letting my broody hatch 4 eggs for the first time, food questions!

Below is a video of my broody hen who is hatching 4 eggs for me, the father is a BC Maran .
This is my first time doing this and I've decided to leave her in her nest in the coop. should I leave her nest 'open' or should I build a pen around it that I can take down after a week?
Also is it okay for the chicks to be eating the flock mix I have out? (they all are fed 50% starter/grower 30%layer and 20% scratch/mana pro... grit and calcium on the side) not sure if I need to worry about anything other then how much calcium they are getting

The calcium is the concern. All the studies that show excess calcium hurts growing chicks use pure layer as their only feed. I have not seen any that use a mix like yours which is going to reduce the amount of calcium they get. It’s not what is in one bite, it’s how many grams of total calcium to they eat in a day, and how many days in a row they eat that. The risk of excess calcium is there but it is a lot less than if you were feeding pure layer. I don’t know how much calcium they are getting from your scratch/manna pro portion either.

Another factor may be forage. Do you let them free range or at least forage on grass? I find that a broody will feed her chicks some feed from the feeders but mine take their chicks out foraging for most of the day. That greatly reduces how much total calcium they get from the feed each day.

Personally I would not feed the Layer in that mix. I just don’t see the benefit since you are relying on the oyster shell anyway and the other two portions should provide all the nutrients they need to lay other than calcium. Why take a risk when there is no real benefit? Especially if the hen takes them out foraging a lot I’d think your risk is fairly low though.

You can leave the nest open, you can pen her in for a week. It really doesn’t matter. I always wait until the hen brings the chicks off the nest. Sometimes I just leave them be, making sure there is food and water for them where they can get to it. Sometimes I move them to a coop/pen outside the coop but in the run for a couple of days before I let them roam with the flock. That’s just so the hen will take them to sleep out there instead of in the main coop when the main coop is fairly full.

they have a large run for free ranging. the reason for the odd mix is i had a bag of layer left over. i used to feed just layer but i notced my hens didnt like it and i have a mixed flock of ages and a roo. i read about feeding starter/grower is best for the mix. thanks for all the info! this is a new chapter for me