NX300 was indeed my first NX camera, and I do miss it, as I believe it a stellar performer, very well built (very sturdy on the hand) and in my opinion, the best of the Modern Retro NX approach.
As you may have noticed, I propose this camera a lot, as I believe it is one of the best value for money offers on ebay currently, best NX value for money for sure, as you can find good ones for as low as 150$.
Fast zoom lenses aren't cheap on any mirrorless system, or they are not at all.
Sony/Canon/Nikon (duh!) have no fast 16-50, m4/3 have - ain't cheap and ain't as fast as 2f in APS-C - they are 2.8f on a much smaller sensor, Fuji's one have no IS and it is an old design (they have to bring something better here) and still is very expensive, there are 16-50S zoom going for really cheap from time to time.
This lens is keeping me firmly on the system (and ergonomics, menu system, small details, battery life, exactly the lenses I want, and a few others).