IMO...I don't think it's too early, but certainly not the best time. Ideally, you would want to stock them just in time to get settled in for their first spawn. If you would stock now, I would take into consideration that some will become winter time snacks before they could reproduce and stock extra. How many extra I don't know, it depends. And, you can not stock too many unless your budget gets stretched.
My two cents.
