RE: sails for the s-type
You might want to check out the product specifications online here for the S-Type 104 to see Starboard's sail size recommendations. If one was to strictly follow their guidelines, a 6.5 would be the largest viable sail. However, if you elected to consider the iSonic line, either the iS94 or iS101 would give you a much better shot of using a 7.4, but maybe at the expense of the 5.0 with the iS101. Much depends on the wind conditions most likely found at your locale, and also your weight.