The Apple Remote Desktop package is installed on the client systems, and not on the server.
If the goal is screen sharing and not the other functions of Apple Remote Desktop, then the purchase is probably unnecessary.
macOS contains both a functional screen sharing client — providing analogous capabilities to what Apple Remote Desktop provides there — as well as the necessary screen sharing server package.
Apple Remote Desktop adds a number of features to the integrated screen sharing client, including ways to maintain lists of credentials for multiple target systems, as well as the ability to push out shell commands without invoking ssh from your own scripts, for instance. It's rather more than screen sharing.
Kickstart is useful when you need to gain access to a system (macOS client or macOS with Server.app installed) before you can configure and launch the ARDagent screen sharing server yourself. It's a way to get the ARDagent screen sharing server running on the target system, usually starting that ARDagent software from the command line. That then gives the Apple Remote Desktop client on your Mac or the screen sharing client on your Mac something to connect into.