A dSLR is, fundamentally, a very, very simple thing to use. You set ISO, decide on aperture and shutter speed, you frame, focus and: click. That’s what you need to learn to take photographs. Everything else is bells and whistles, you’ll figure it out as and when you need it.
I’d recommend getting the best Nikon or Canon dSLR that fits your budget, with either a 35mm or 50mm prime lens (maybe switch 50mm for 24/28mm if you’re doing lots of landscape). I don’t know Canon, but stay away from 2nd hand Nikon D600 unless they seller can confirm that Nikon have replaced the sensor/shutter seal (international recall).
The D6** series are full-frame, everything belies that is cropped (roughly 1/3 off your lens’ focal range) – a 28mm on a D3300, for example, will be equivalent to a 35mm on a D610.