I do not mean to get the cheapest one. I mean to define what a monitor/features you want and are worth for you. Are you running a studio for fashion photography for a magazine? Or it is a hobby.
In my opinion, the best monitor to have is the one you can purchase now and not in an undefined future.
Yes, size matters. Are you ...
Things NOT to get:
TN panels of any kind. Their color rendition varies on viewing angle. IPS and its variations (including PLS and AH-IPS) is what you want.
Any monitor that isn't at least specified as 100% for the colorspace you want to work in. Might calibrate to 98% or so of it... still, far better than a design that does not try.
Monitor(s) your PC ...
Usage scenarios where having both is handy:
I primarily use raw, now that I've found that the space hit is only about 50%. E.g. A raw file for my Nikon D7100 is about 30M, while the high quality same resolutin jpeg is about 20M.
I set the camera to write raw to one memory card, and jpeg to the second memory card. This gives me a backup if I have a card ...
I always do the color grading stuff before, because if done after retouching it can make the editing more visible. The edited parts are always a bit different from their surroundings and will react differently to the color tools.