Rookies, what do you want an X-T1 system for ???
- If it's compactness then the 18-55 is the way to go, it's a brilliant lens, and makes 'kit' lenses from other manufacturers look daft.
- If you want the ultimate zoom in that focal length band then the 16-55 is the way to go, but, it's a huge (in Fuji terms) slab of glass. - the 50-140 is equally a huge piece of glass, but to get constant f2.8 out of a zoom there are physical limitations.
- But if you want the best IQ then primes are the way, the Fuji primes in this band are excellent especially the 23mm and the 56mm.
You really do need to make your mind up about the hardware direction you want to take your photography in.
In your shoes, I would buy a S/H X-T1 and 18-55 and see how you get on with the Fuji system. Explain to your wife that after 3 months you will sell either the Nikon or the Fuji, and for the moment she has to let you use both systems side by side.
You may not even get on with the Fuji way of camera handling/menus/etc, and if you decide to sell it in 3 months you'll probably only loose £30-£50. That is a small price to pay to the amount of time you spend analysing every detail on forums. Get out there and do some shooting, get a life back and stop trying to spec a camera system off other people's opinions,.....this is not a risk free hobby......what one person likes doesn't suit all.....