BuildPacks are like addons except it's expected a user will have a full project lifecycle involved with it rather than just booting up a pre-made instance when needed. Buildpacks can incorporate a set of libraries, language versions and more.
Projects are composed of images and base volumes. Instances are running or paused copies of both the kernel image and volumes. We will keep your base volumes that are associated with a project until you remove the project. You may always back up the volume or clone the project before deleting it too.