I'll try this one.
The basic rig of our fractional boats is the forestay and upper sidestays. There are wire tension figures for these wires published for your boat in particular, and also maximum usable tensions by wire diameter. For example, if you wish to use a higher tension for competition, your overall tensions will exceed what a family outing tension would be....
After the upper 3 wires are tensioned correctly, the 2 lower sidestays are next. These wires serve to straighten the mast, as the upper 3 wires may have compressed and bowed the mast forward between the deck and the hounds (where the forestay attaches to the mast). The lower sidestays allow the mast to be straightened. No particular tension is used here- if the mast happened to be straight after tuning the upper 3 wires, the lower sidestays would have zero tension.
Finally we reach the backstay. One intent of a fractional rig is to be able to bend the mast aft with the backstay (which flattens the main). If you do not have the ability to adjust the backstay tension while sailing (with a block and tackle), then the approximate backstay tension should leave the mast straight ABOVE the hounds, with the least amount of slack.
When I say the mast should be straight, I mean that one should lie on deck and sight up the mast along the aft slot in the mast. Of course, on the initial tensioning of the rig, the mast should be equal in the side-to-side dimension.
The mast is strongest when it is straight. The stresses on our rigs tend to drive the mast down into the deck. The rake of our masts are pretty much determined by the length of our forestay, once it is cut to length. The forestay turnbuckle determines the rake adjustment (if any), and then only if the sidestays can accommodate the extra length or shortening.