In one of his great books, garden writer Henry Mitchell comments that
tourists love to visit Versailles, and comment on what amazing gardens were
created by King Louis the whatever. They forget that except for the statues,
the beauty they're seeing is due only to one thing: The labor of the people
who cared for it yesterday, not hundreds of years ago.

Perhaps the previous owner let one season go by without doing the necessary
work, hoping it would care for itself. As another person here suggested,
limit yourself primarily to maintenance and observation this year. Take
pictures, make notes, walk around with catalogs & books and identify what's
there.

Have a couple of beers. Things could be worse. You could be one of the
unfortunate people who doesn't have a garden at all.