Hi there,
Your requirement is pretty clear. Though you want to use php for this, if it's not a hard requirement I highly suggest python with scrapy. It's a much more stable and robust choice. As long as there's enough amount of accounts orders to be placed is limitless. Proxies, emails and gift cards are all fine but changing mac address is not necessary as it's not exchanged with http.
I can start as soon as you award the project and expect to deliver a tested solution within 8 days at most. As I've mentioned I'd prefer python considering your requirements. Still if you want to go with php that's fine as well.
Thank
Aydin