Can you add eggs under a broody hen a few days after she starts brooding

[TheOddOneOut]

I had a few more questions I appreciate the help since this will be the first time I've had a hen hatch out chicks, when she leaves the nest do the chicks follow her and will she be able to look after them herself or are you supposed to help in some ways?

Do I need to keep them all isolated from the rest of the flock like fence off a corner where the hen and chicks can run around in or will they be ok with the rest of the flock? She's the top of the pecking order and the other hens are fairly docile the rooster too is friendly natured if that makes any difference

Can I still feed her grain and layers pellets like usual and will she then feed that to the chicks or do I need to put down some chick crumb?

Do you still need to candle eggs to make sure there's something growing in them and remove any duds - if she sits on infertile eggs will they explode like in an incubator or will they just not hatch?

Thanks

She, for the most part, will do most of the work.