Re 20 inch wheels.
In my opion a 20 inch wheel folder will handle signifately better than a 16 inch all things being equal. Particully in the cushioning of bigger tyres. But a 16 inch folder is much more compact folded, hense their populatity for commuting. Top 16" folders can handle well enough. I have 4 16" folders and one 20". The 20" downtube is a hudge unweildly package compaired to my other bikes.