My thinking here is virtually any video will do as my video requirements are more likely to be definded by other softwares requirement rather than a DAW
 
Also I'll probably go for a single monitor configuration as I probably couldnt justify a second monitor. Also 4k & 8k are not a prioity......... So what size should I go for and what features are a must

Not trying to persuade you, but having two monitors is really a helpful thing. One can be used tracking/editing etc. while the other for mixing.....it just expands your real estate vastly. A couple of 27" or 24' monitors (1920x1080) can be found for under $200 ea.  
 
If you're going for 1 monitor, then possibly 1 big monitor would work well.