For all the reasons you mentioned........I wouldn't recommend a silkie. A better broody for you would be a Buff Orpington. My BO went broody 4X last year and I'd have to give her fertile eggs, let her sit (and give her feed store chicks) OR try to break her broodiness. But if you WANT a good broody.........I personally think Buff Orpington's are great! My Buffy is a big girl and can cover a lot of eggs and she is a great momma.
By the way -my silkies have never gone broody for me! They don't even act like they like laying their occasional eggs.
And, yes they are very fragile and have to be kept seperate from my large fowl girls. Any of my LF hens could beat the snot out of my little silkie rooster if given the chance........I hate to think what they would do to my little silkie hens.