Loops are known to be low noise antennas. For  resonance, they should be cut so the total perimeter of wire is one wavelength at the lowest frequency of operation. The formula for loops is a little different than for other antennas as end effects do not have to be taken into consideration. 1005 divided by the frequency in megahertz will give you total wire length. For a receiving antenna, resonant length is not a concern. Just put up as much wire as possible. Use of a balun at the feed point is a matter of debate. Some say it is beneficial and some say not. In any case, the use of one could not hurt and I believe it could be beneficial as it retains the symmetry of the loop and avoids directly grounding one side of the antenna. In any case, the coax should be brought strait down to the ground and grounded to a ground rod at that point.