Take Off Field Length, ISA, SL, MTOW7, 2,270m
I wouldn't worry about taking the ERJ145 into ZQN, those takeoff numbers means that AKL and CHC will be the only fields it can operate at Max payload.
I checked with a pilot friend flying P1 on the ERJ145 and he confirmed those numbers so this operation is going to be very limited with where they can go in NZ.
The reason for ERJ's is that they are cheap because they are not cost effective on short run operations.
Only AKL has the capability of Cat2 (as of 02 Aug 07) or 3 (sometime 2008), and when operating at Cat2 movements are limited to 6 per hour until ground radar is available (2009). International Widebody operations will have absolute priority for low viz operations.