No idea with your mousse... try it and see what happens!!
I would weigh your chicken in its raw state and defrosted tbh, then you know you are having the right amount.
don't know about the gelatine thing but i get the mix a mousse from my cdc and have 1 everyday. I LOVE them. Just had a chocolate 1 as it happens and it really tastes like a proper 1. I also like to have half banana and half toffee and walnut, that tastes like relly yummy custard.