About 4 weeks ago I was feeling exactly how you are now. No idea how to start. I watched the fabulous 3-DVD set World Domination Gardening https://richsoil.com/wd-gardening.jsp
where they filmed digging a pond, a swale, hugelbeds, and even footage with several newbies running the excavator. That was *extremely* helpful.
Then I googled "Crater garden" and "Krater garden" and watched every video I could. I listened to this presentation by Zach Weiss which is similar to his "Renaturing the Land" podcast, but this one gives a wee bit more info about the Crater gardens: https://www.youtube.com/watch?v=qE15UCbXcsY
The quality is not great, but I'm grateful to whomever videoed it! In it he talks a little bit more about trees on the crater garden. They are important, in part, because their roots help the water get down to the pond. He mentions there are additional reasons. I *surmise* these are: shade and that tree roots exude moisture themselves. Fruit trees are planted on the mid level of the garden. Water-loving things at the bottom. Drought-resistant, nitrogen-fixing shrubs/trees at the top. (I'll let you google what those might be for your zone/climate.) He says Sepp says the pond will dry out without the terracing and the trees.
Somehow, I saw someone digging a little fish pond with a compact tractor so I searched for videos of "digging pond compact tractor" on YouTube. That gave me a lot of hope. At minimum I think I can get the sod stripped off, and maybe the topsoil below it, with the normal bucket, not excavator...don't have that attachment. If I can't handle the heavy clay, then it'll be time to rent or hire someone. We'll have a builder here next summer finishing some construction, so I might be able to talk him into it.
Lastly, there are some excellent and inspiring photos of Crater gardens and other earthworks on Zach's site: http://www.elementalecosystems.com/#projects