RE: 4 inch or 5 inch fletching
I am more partial to the 5" feathers, mainly cause I like more surface area on the fletch if I am using a fixed blade as yourself.
But if you plan to only shoot to 30-40 yards or so, I don' t think it will matter too much. Past that is where the difference will be more noticable.
I would suggest getting some sort of helical or offset either way though.