Glad you mentioned monitors as I forgot to say I think a good monitor is just as important as the machine itself.
Personally I would try to avoid glossy monitors as they can make it difficult for your eyes to focus on text.
HiDPI/Retina are also worth it imo, and personally I recommend getting a larger display so you can push it further away.
When my LG5K monitor broke last year (common TB port issue) I tried to fix it but ended up killing it 
(though got a semi-fix by buying a second hand one and swapping the motherboard - it works now but only on full brightness, which is bad for your eyes) so I bought an ultra wide 40" Dell, and I love it! Not because I can cramp so much on display, but because I can get enough of what I need and place things evenly with nice gaps. If you’re into things like Feng shui you’ll appreciate a monitor with a lot of real estate. The other thing I have done is download a massive amount of HQ desktop wallpapers, and set it to change every 5 minutes, This means every time a nice landscape image appears I get the feeling of being outdoors, can focus my eyes on things that appear to be in the distance etc. Only problem is after a while you yearn to be out in the real world!!! 
For anyone interested, I highly recommend https://wallscloud.net/en for wallpapers, easily the best site of its type around. I have my resolution bookmarked and check it every day.
