North 2 was originally used as a VHF cross over to north 3 on the 450 system. It is still part of the Marion County Fire template and as Comms13 pointed out is not used a lot. North 3 and 4 came about in the early 2000's when there was only one channel for north county (Aurora, Monitor, Woodburn, Hubbard, Mt Angel, Scotts Mills, Silverton Fire, St Paul and Woodburn Ambulance) for both dispatch and working and it was a busy cannel. There was one district that would come up on the radio anytime they left the station (as they should) but let say they were going to get fuel, they would announce they arrived at the fuel pumps, grocery store, etc. It was a bit much. North 3 and 4 were originally on a privet LMR LTR system, and then WFD built there own LTR system at the same site as the privet system. When North 6 and 7 came into play the UHF system was not needed as much.
North 5 was the old channel for Silverton Ambulance before they were merged with Woodburn Ambulance. Silverton Fire kept the license (that was a smart thing to do) and it is also still part of the Marion County Fire template. Silverton Fire also has Ops that they use like North 2.
Well I can't comment on the new system, I can say that the Tait subscribers are not making a great impression with the users that have them now.