Staging a switch stack before deployment

I have a customer with an 80F firewall deployed with a Cisco switch stack. We are getting ready to replace the Cisco switches with 4-Fortinet FPOE switches. I would like to stage the equipment and redo the configuration in the office using a 80F which is not registered to anyone yet. This firewall will be returned to inventory after the staging.

I am wondering what obstacles I might encounter when performing this staging of equipment.

I have upgraded the 80F so that the firmware matches my customers FW. The plan is to provide basic access to the Internet to the staging FW and then register and authorize the switches. The disconnect the FW from the Internet and 

rebuild the customers rules after assigning the VLANS to the FW. Any help advice would be appreciated.