A bit of followup.
Comcast issued the 5 IPs. 
Comcast placed the unit in bridge mode by disabling DHCP, firewall, and few other things.

By the time I got onsite, the IT guy was able to grab first of the static IPs, put the DNS settings into his firewall and he was done.

Me, not so much :-(
I have never had to do that with 750 so I struggled.
750 is so powerful that it makes it a challenge for new things. 
Without Internet access onsite I had hard time trying to figure out on my cellphone how to get things going.
The IT guy even tried to help but he's unfamiliar with Mikrotik.
Frustrated, I left and I'm still doing research at the office at 1:30AM. 
Jayson from IP has been very helpful and I hope I can get things going in the morning.

IT guy even told me that he'll read up on the router for his own learning/knowledge and to assist me if I still have issues.

I will followup when I succeed, because one way or another I will succeed.