The MH axles are great. Most of the reasons people don't like them is because of the odd-ball bearings, hubs, wheels, tires, etc. But, if you have a source for them, they are just fine for a utility or car trailer that sees intermitent use.
Yes, do get new tires that are DOT approved.
To get a tag and title for a trailer in NC, you will need to go to the tag office and tell them you have a home-built trailer and need to title it and register it. They'll ask a few questions about it (size, capacity, etc.). Don't tell them it came from SC as that will be more of a PITA for you. Tell them you got a used home-built trailer from a friend. They will give you a VIN and you have to stamp that on the tongue and at least 1 of the axles. Once this is done, take it to the tag office for them to inspect and then they will issue you a title and registration.