Is this meant to be possible? Kind of mean to have to also invest in a second building just to sell my stuff 
You mean you only have a single socket in the room you start out with? Any socket is Input/Output depending on what you choose to do with it.
Yeah I only had one socket so I’m not sure what exactly I was meant to do in that room other than run myself into a huge loss 
Although, interesting to note what you said - it wasn’t clear to me that the sockets were multi-purpose, since they always look like either import or export and I don’t think the tutorial mentioned this.
I’m sure it’s an unintended flaw in the map generator - I can’t think of why Tim would start you out in a “room” with only a single socket. 
But yeah - Any socket can be either Input or Input. Only depends on whether you tell it to import an ingredient or not - If you extend belts from a Pill Machine, Creamer or Injection Maker into a socket, it will function as an output socket (sales)
You can even change your mind later and stop imports in a socket and rearrange your machines so it works as an output instead.
There are some rooms in some of the maps that have no sockets at all, and then some with 4-5 sockets. But I’ve yet to get a starting room with only 1 or no sockets. Think the map generator just need an extra check to make sure you start in a valid room.