Shorten forestay (Harken) or backstay?

[sharkdiver84]

I noticed this problem immediately after purchase. All the rigging looked good, but I didn't think to check the forestay tension. It was unbelievable loose.

Harken has a video about how to tighten the turnbuckle, but there's only a turn or two left at the bottom, and I'm struggling to get the screws out of the plate without boring them out.

I tightened the backstay to max, and it's still a bit loose for my liking. Now the question arises, which stay is too long? Shortening the backstay would be easy easier, but I assume this could mess up my sail plan by adding too much rake. How can I know for sure though where the error lies? Is there a good method to determine whether the mast is angled properly fore/aft without buying expensive tools? Would it be extremely difficult, or impossible to shorten the forestay mostly single-handed without dropping the mast? I'm presuming that means resizing the foil as well. The boat needs to be useable very soon, for as cheap as possible, but doesn't have to be ready to go around the world or race.