All purpose lens help needed
IMO, 16mm is supposed to be used at larger aperture. Landscape is the primary point of such lenses to begin with. That it can be opened up to f/2.8 is only a convenience. The same argument applies to my choice for ultra-wide photography: 8mm f/2.8 Fisheye. It is a lens I prefer to shoot at f/5.6 for its DoF. I reluctantly move to f/4 and f/2.8 only if the shutter speed gets overly demanding (1/5s or less).
As for 35mm/1.8, IMO, it is a nice focal length, and the ability to go f/1.8 is nice under low light, something that is limiting with kit lenses.
If you must decide between 35/1.8 and 16/2.8, then I'd say that the 16mm is disposable as you can almost reach the wide angle view of 16mm with the 18-55 but you will have the benefit of brighter lens at a very useful FL with 35/1.8.