RE: Problems going upwind
OK, here are some suggestions:
I took a look at the Maui Sails Website and I'm not so sure that the 8.5 m2 Pursuit is really a good match for your F-Type 158.
That's all I'm going to say on this subject.
You need to figure out how to get back into the outboard and rear most footstraps. Using the inboard and forward footstrap positions is taking away alot of the leverage you need to set the fin attitude to take you upwind.
Your harness lines sound as if they are too long for you to get your weight off the board and onto the rig.
Especially with your footstraps forward and inboard, you can't get your weight off the board and I would suspect that you are indeed pushing "down" and doing it with your heels (or at least the heel of your back foot. On a board as wide as the F-Type 158, there's no way you can get the lee rail lowered a bit and pressure on the fin to go upwind on fin lift, so you are probably using upwind rail down and the shape (rockerline) in the board to take you upwind slightly.
This of courese slows you down dramatically and prevents your board from really getting upwind in the way it was designed.
If the board seems to be going sideways, I'm absolutely sure you are trying to use the upwind rail.
You need to really get the board going, get the rig fully sheeted in and the foot of the sail down on the deck (you are correct, you cannot check your harness line balance with the sail raked back and down until you are on the water and you can remove one hand from the boom, and if the rig seems balance, then take both hands off the boom momentarily. If your rig is truly balanced, you should be able to take both hands off and the rig will simply stay in the same position and provide you with the same power, either hands on or hands off.
I'd try your mast foot a little further back, but wait until you have acheived getting the footstraps moved back and out board.
My guess would be that you have only "scratched the surface" of the speed and upwind speed and angle the F-Type 158 is capable of.
Hope this helps,