XPS 8700 Suggestions please - two interim replacement parts needed

Suggestions please

Hi guys,
I will not be in a position to buy a new Dell system for a year, and I want to ask what people would suggest for two interim replacement parts in Feb 2017 for my reliable (mid 2013) XPS 8700  - i7 4770@3.4 24Gb DDR3; 256SSD, 2Tb HDD, 1023Mb nVidia GTX650Ti .... BTW I use Win10 Pro.

MONITOR

Firstly, and importantly my good 'ol 1920x1080 monitor is on the way out. It is getting urgent I replace this first and soon.  But it needs to work well with my next Dell system too!  So, I am starting from this position. 

I am suggesting a replacement with a 24-27" monitor that can handle 4-5k Colour. However I note that some people seem to be advocating staying with a good 1920x1080 display for sizes under 27" and forgetting 5K. However, I can afford to get a higher pixel count as long as I can resize things to make it readable on the screen.

A must is that it will work well with the next Dell system that I intend to get in first/second quarter of 2018.

I need it to have at a non-HDMI connection (Is that a Displayport?)
I need at least three inputs to handle plugging in various devices like AppleTV, or TV hardware, or (future) Bluray player or even HDR capable..  I presume HDMI.

My uses:  General Internet, WP, watching movies, and rare but neccessary ability to run Elite Dangerous.  I also use it to do family/church  videos and audio editing. I don't specifically need accurate colour, just good sharp pictures that dont blur.  BTW, the monitor does not need to be Dell.

Graphics Card

I think it's a given that the existing GTX650Ti will not have what it takes to supply a new monitor, especially if 4-5k. 
I have received one suggestion to replace it with something that will work ok  with the monitor until 2018 and the new system, and that is a EVGA 550G2, but I don't have the knowledge to go with whether it will fit, or either the load on the Dell's PSU will cause noise or overheating - even just playing back a movie.

May I request helpful advice please guys?
I don't know how long my monitor will hang on...

Thanks in advance

Pete