*You're thrown a typical webdev task, like setting the filesize limit for user u...

You're thrown a typical webdev task, like setting the filesize limit for user uploads.

That's a web server configuration, not a programming issue.

Connect to MySQL and store some data.

  (with-database (db '("host" "db" "user" "pass") :database-type :mysql)
    (insert ...))

With CLSQL. http://clsql.b9.com/documentation.html

Now determine the dimensions of a jpeg image.

CL-GD has image-width and image-height functions. http://weitz.de/cl-gd/

And parse some JSON from a file.

In my world, json is rarely read from disk files. It's passed around between client and server. At any rate.

  (with-open-file (file path)
    (let ((json-buffer (file-length file)))
      (read-sequence json-buffer file)
      (decode json-buffer)))

http://common-lisp.net/project/cl-json/

You are showing a complete misunderstanding of software engineering. You don't go running around looking for examples and installing 3rd party packages willy nilly. Weird problems don't just "arise" out of the blue, and although there is some urgency to things there is never any chaos. Things are a bit more controlled, and you are assumed to know what you're doing, Lisp or otherwise.