The optimum gain of any antenna with parasitic elements varies with the spacing and tuning of the antenna's elements. This ALWAYS require manual tuning and optimization.
It is very unusual for the optimum front to back ratio matching the same condition that gives maximum forward gain; some compromise is probable and is in order. The impedance of the driven element also varies with all tuning and spacing operations. Hence, the antenna system must be tuned, probably several times in small increments, to its final condition before the final match between the coax and the antenna can be completed.
The antenna can be fed directly with standard coaxial cable (RG8/RG58) 50ohm unbalanced, however, in most cases a 1:1 balun is used to significantly improve matching. It should also be noted that for vertical polarization feed, the driven element is fed from the side of the diamond or square, and for horizontal polarization feed the driven element is fed at the bottom of the diamond or square, depending on your mounting orientation.