Transferring existing Fortiswitch and Fortiap to new Fortigate

Setting up new Fortigate and prefer to start from scratch as old gate was breached several times most recently during the SSO vulnerability and changes were made. Instructions that I could find recommended deregistering and wiping configuration on the old gate and resetting and programming on the new gate or transferring the relevant configuration to the new gate. Is it possible to leave everything as is on the new gate, wiping switch and ap (resetting) and then attach to the new gate and setting up from scratch or will the fact that it is still set up on the old gate interfere with the process? Would just prefer that I have the option to put them back on the old gate if I run into difficulties with the new set up. Clearly not a network engineer! Rolling back to 7.4.12 on new gate because of glitchiness on 7.6.7 and switch is on 7.6.6 and ap is on 7.6.5 - should I drop back firmware on switch and ap when I transfer them?