before that u should give us your budget..else ppl will tell u the 3 trinity and D4s 
where to get? i think best still getting local set. Even getting AP set, get from a known seller that can help u settle the warranty issue if encounter anything.

Nikon's mirrorless systems are not that good when compared to competitors
So if you want to stick to Nikon, DSLRs are still the better pick 

Mirrorless cameras, as the name suggest, lacks the mirror that allows you to see what you will be photographing through the lens- they lack the optical viewfinder, and thanks to that, they can be designed to be much smaller and more portable
Of course, smaller = more portable but less ergonomic

So it depends on what you really want most mirrorless systems nowadays are quite affordable, and uses similar sensors (go for the ones with APS-C and not m43) as those in DSLRs.

If portability is important to you - mirrorless
If ergnomics (dials and button layouts) - DSLR

just my 2 cents~

not really true some higher end mirrorless have quite many custom buttons that allow users to pick a specific function for them. thus it will offer more direct access compared to dslr.

the main advantages of dslr I can see compared to mirrorless is the phase detection, weather sealing/ ruggedness and also the choices of lenses (not really matter if you just shoot specific thing, not everyone buy every single lenses of a system anyways).