You don't have a problem yard, you have a problem tree. The wooden porch thingy was probably perfectly well built to begin with but the tree's roots have lifted and broken it. Same with the landscape ties beside it. It's coming for your house foundation next if it isn't already doing some damage. Good thing it's your tree and your house that's closest, because if that were not the case there would be some potential liability issues here - all you've damaged of your neighbours' is the retaining wall, which will be easily rebuilt once the tree is gone. See the slope of your front yard in the second picture? That's all tree root effect.

The very cute cobblestone walls are simply at the end of their lifespan, which has been shortened by trying to hold the front yard together under pressure from the tree roots. But news flash: this is not a rock wall, it's a concrete retaining wall decorated with rocks. So when you go looking for a book on how to build retaining walls, follow the directions for concrete, not dry-stack stone.

A slope is not problematic in and of itself, in fact it is a huge feature if you design that way. You could, for example, make your vegetable beds there, a series of raised beds going up the hill like steps, with actual steps beside and between them for you to go up to tend them. And no, the east side of the house is no place for tomatoes, they need full sun.

What you have here is a charming little house on a great lot where the landscape installation is simply at the end of its useful life. What needs to happen here is the setting of priorities and the making of decisions. If the structural integrity of your house is important, the tree should be taken down pronto, and then you have some hardscape rebuilding to do: steps, walls, vegetable beds; whatever your vision for the place dictates. If you are at a bit of a loss, some reading through the landscaping section at the library is always a good first step.

KarinL