The data sent over the stream is pre-selected. The limitation is that Outernet is one-way, you only receive, you don’t make requests. It’s not an internet connection.
The link you posted is 404 for me as well. Outernet isn’t currently on the air, and the next generation of the receiver isn’t released yet, so there are no OS images to download and install, because there’s nothing to install them on.
The receiver will be released soon. A Raspberry Pi is not part of the receiver, buying one will not help you receive Outernet.