Hello, yes that's the best way, the amount of eggs that fit in your incubator wait till you have that many eggs and put them in all at once, that way you have no headache or worries and they will hatch at the same time! Good luck :)
Well i think you will be better of if you put the remaining eggs in a incubator and the chicks that have hatched put them in a brooder and raise them yourself.
Yes, but you should leave the last 3 eggs, because normally when hens break a egg they no its empty, thats what i have learnt in keeping chickens all the ones my hen use to break was non fertile, was the egg empty that she broke?
No i dont think she will take the chicks, chicken are clever and very protective, if a new chick will come by her they usually dont look after it or will eventually kill it.