Thanks all. Some great suggestions. Stupidly I have an eBay search set-up for a Nikkor 70-200 but hadn’t even thought of looking at lenses…
What is the D7200 lacking? Not a lot, TBH. I also have a D300 as a back-up which is an awesome camera; it was replaced because of the advances in low light performance (the D300 shows its age here) and to get double SD ports. So, to compare the two, I do miss the auto focus button on the back, the D300’s more solid build / weather resistance and slightly higher FPS (with additional grip: 8fps vs. 6fps). But otherwise I cant fault the 7200 (well, maybe a larger buffer wouldn’t go amiss).
Going FX will probably happen at some point. Unfortunately I can’t buy bargainous second hand with this particular deal, so a used D4 is probably out of the question at this point. But it doesn’t hurt to have a goal! A lens would be a good start.
Again – thanks all. This has helped sort out a few ideas.