I have done what you are thinking about in digging down and adding stuff from around your place. I then
went pretty much with Emelia Hazelips measurements. Beds 4' wide 10' to 30" high and paths 20". She got
out a pointer to emphasis this in her youtube video and repeated it. So I took that to be something she valued.
She tilled to start and used soil from the paths to build up her beds. I used soil from the paths, soil from the hole
and added
compost to the top layer. Then I mulched with wheat straw. I am interplanting and trying to get a good
mix of plants in each bed in hopes of confusing pests and minimizing problems.
The final two beds were done on top of the soil piling up what was left in the yard and then putting leaf mold. soil
from the paths and compost on top and mulching with wheat straw. This performed very well with very nice peppers
and eggplant. I also had lettuce and basil and each bed had one cage of tomatoes which did good. I would think that
long term digging down might be a better solution but this was quicker and easier and worked about the same.