You will definitely want to do a fair amount of planning and schedule an after-hours change window because there will be some downtime. You'll need to configure a transit network, configure the SVI's on your switches, if dhcp was previously coming from PFsense... you'll need to figure out where your new DHCP server is going to live, add helper addresses to each SVI, change the default gateway for all of your dhcp scopes, change the default gateway for all static devices, etc.
There's quite a bit of work to do, but it will be worth it.