Hi Simon, beautiful looking property.
1) Land is hardly ever flat, find the contours using an A-frame level https://www.youtube.com/watch?v=g0DxX2d4L0A
which is extremely easy to build and use. Swales will work best to slow, spread and sink your moisture into the ground. Plan fully the entire area before doing any work or you may have to undo what you put hours into. Swales can work really well for generating a food forest--see attached photo.
2) I"m not sure if that was Geoff who said that, but considering the small size of your property and the relatively low profile, I would go small.
3) It is said "do your earthworks first". This is good practice and will help develop your food forest. Swales will create a zone to begin planting your overstory, establish crops and ground covers.
4) I don't think you should have too much of an issue increasing nutrients on your property. It looked like you have a lot of organic material that can be put to good use in creating a very healthy forest floor. Remember that not all you initially plant in a food forest goes to production, a majority goes to benefiting your future food producers.
5)not sure about this. what are others in the area building? What resources do you have at hand to build a sustainable building with?
You also mention using hugelkultur. While it is great for retaining moisture for plant beds and also creating wind breaks and privacy, the main function is long term--to break down large amounts of organic material that are otherwise without use and eventually use that to benefit the surrounding soil. I wouldn't focus too much on doing hugelkultur unless you have a lot of large timber or brush that can't be used as mulch directly.
Post photos--it sounds like an awesome project.