Certainly @KA that's fine. Depending on which 3rd party APs you're using, you can either have DHCP services provided by the MX, or by the standalone APs if they're able to do so. Regardless, like you said, clients on the APs would benefit from the security features of the inline MX, just connect the MX68 WAN to your ISP and hang the APs off of the LAN ports.