On an H16, when you hoist the jib the forestay becomes slack. This supposed to happen. You now end up with the jib stay holding the front point of the boat with the shrouds holding the side. Do not adjust the forestay after setting the forestay. You will only have to readjust it to unstep the mast.
As for the proper tensioning of the jib and shrouds, there is a lot to read. Too much for me. I go with what feels right making sure that the mast is properly supported.
John
Palmdale, CA
H16