The answers to all your questions are basically it depends, except for the soil around a maple tree, which is likely to be fairly depleted of nutrients.
In general, the starting questions for gardens are:
1) What do you want to grow?
2) Is this plant suitable for local soil and climate?
3) Will I need supplemental water?
4) Will I need to amend the soil?
5) Will the plant get enough sun in the location planned?
6) What cultural practices will decrease the amount of predation and disease and insect damage for this crop in this location.
The book I tend to recommend for new gardeners is the old Rodale Chemical Free Yard and Garden, which can be picked up dirt cheap as a used book. For more specialized information, if you’re in the US, I recommend local extension service and master gardeners as information sources.
There’s no use spraying or treating for problems that don’t affect what you’re trying to grow. And no magic elixir that will always guarantee a crop.