I honestly say you got two ways to go about figuring out what works best for you... 1. like i said earlier - stay where you are now and go ahead and get the white ameracauna you're planning on - and wait a bit and focus on those, then see if you're ready to take on more the next year or whever... OR 2. get the full load you want and work on seperating them out, getting together the good stock of each breed, and try working on them.
my only thing is you're 15 - so what do your parents have to say about adding a bunch of breeds, coops, and pens? Are you going to have the money to keep each variety/breed seperated out put the money into buying the best stock you can of each breed/variety? How about space? pens, coops, incubators, brooders, etc... I believe to achieve and be able to produce a nigh number of quality chicks especially in the first couple years as your establishing your lines (as this is your goal) then you'll be needing to hatch and breed up as many babies of a breed/variety as possible.
Honestly your young, you still have a few more years of school left, and from personal experience it only gets more hectic the longer you're there...I honestly just don't want you to try and burn yourself out with taking too much on too soon. I believe taking too many on too close together before atleast establishing your stock and breeding programs with what you already have isn't going to allow you produce as good a representation of the breeds as your looking to achieve.
I'm just saying focus on what you have now, and so getting your breeding programs for them straight, and making sure you've got the best breeding stock as you can afford, and thus you'll the best available to work with breeding off of. Then we you get your current (and white ameracauna) good and settled with before adding another breed. I just worry with a bunch too early on you're not going to be able to pay as much attention to the type and quality of each breed and will be spread too thin.
Anyway hun, good luck and I hope everything works out for you. Just remember your young and you'll have time to get where you want to me, theres no need to rush!