Chickengeorgeto is right - as long as they are pretty much fully feathered your younger chicks should be fine to sleep in the outside coop. My 'golden girls' were doing fine in the outside coop this spring at 5 weeks old.
I have never heard of a rooster collar to stop crowing, and to be honest it is not something that I would ever consider, as I do not agree with anything that prevents natural chicken behaviour. It is only a personal opinion, but I believe that if you have to do something that modifies or prevents a bird's natural behaviour (debeaking, wing clipping etc) then your birds are not happy. If birds are kept in good conditions with enough space, feed, activities etc. then they shouldn't peck each other agressively or try to fly away. I only have a 75cm-high fence around my property, but my birds never even think about flying over it - they are happy enough where they are!
I assume that the idea of a rooster collar is to be able to keep a bird that naturally crows loudly in a built-up area without annoying your neighbours. However, I would question the ethics of preventing a rooster doing what he naturally does, just to satisfy our own desire to possess a particular bird.
Please don't get me wrong, BoiseChik, I'm not having a go at you for considering the idea, as I said it is only my personal opinion - others feel differently and have a right to do so.
Keeping more than one roo in a flock is certainly possible in principle, but in practice it depends upon whether the roos get on with each other, as well as the number of hens per roo. Too few hens, and the roos will fight over them, and also exhaust them with "over-attention" (if you get my drift!)