Demountable camper group

Hi all,
I am at a point with my home build where I an ready to purchase the windows.
I am unsure how big and what type. Originally I was thinking Seitz 700mm x 400mm on both sides.
Question:
Is bigger better for interior light but more heat loss?
Are horsebox living area windows suitable/ desirable as they are bigger and a more economic buy?
The money saved on cheaper windows could be spent on a propex heater?

Any idea's suggestions welcomed

Mark

Hi all,
you will no doubt be pleased to know that after all the input I have received on window choice, I have made my decision on which to purchase

Mark

Windows are apparently not our best subject here, I'd have said leitz as on mine as I know them but I'm sure there are lots of other on market