it is better to run dhcp on your AD, since it helps in the registration of clients in dns.. Or can be setup too, etc.
To be honest if your running AD, use pfsense as its primary function routing/firewall.. Stuff like dns and dhcp, ntp are all just bells and whistles for a site that doesn't already have those things taken care of. If your running AD, that is where those features should be setup.
And yes you need to make sure your AD is setup with good time source, pfsense could be that sure. But your going to want to let your AD members sync to AD - once you have setup AD correctly, etc..
You can setup your AD dns to forward to pfsense, but all clients in AD should really point to AD for dns.. Then your AD either forwards or resolves stuff that it is non authoritative for, like pfsense.org, google.com