I live in a very small open concept condo and I decided to arrange my furniture so I always have a 3 feet wide path to move around, and I can say it is a confortable width (for one person). But for two people, maybe less than 2x3 feet is ok, as they make double french doors starting at 4 feet wide... Suggestion : put some masking tape marks on the floor and try visualizing !

I assume the windows abut in the corner? This would make it tricky to have romans as they would probably clash when both drawn up. Curtains drawing away from the corners add softness to a dining area, but make them floor length as short curtains look a bit half mast. It is also a good idea to have them wider than the windows to allow more light in when opened and fitted from above the window to elongate the window.

You are correct the place does and always will look a bit sparse when you only have blinds. The question with curtains is sometimes dependant on what climate you live in and I am not sure where you are so I am going to say. If you need curtains for heat go for a quality curtain to the floor with a fabric that is not stiff (as I discovered I now own after buying curtains off line for my spare rooms). The expensive curtains I brought for my living room have a softer texture and hang so much nicer. As I need Curtains / Roman blinds for heat I have backing fabric etc on the expensive made to measure ones, where as the cheaper ones are just thermals. If you only want to add a curtain for looks and do not require it for heat I would recommend going with a lovely sheer / half see through fabric that drapes really well, this will add a point of interest and you can colour match or add a loved colour to a bare - white on white - cream on cream - colour scheme.

I have a similar sized ensuite in my own house and would definitely not put two doors in it. You will probably find that a fixed glass panel to half the width and a glass door the other half would work fine. Alternatively you can get a sliding glass door (again 50/50) if you like the look of them as they do save on space.