a suggestion:
reverse the count down or change so it just shows a color on the screen, turns on off a set of lights in order (red, yellow, green in that order) you can also have it close and turn off the door until the transaction is complete (may even be able to swap the accept/decline sensors for 2 button panels (2 buttons active, 1 at each end and have them placed so when using you are facing eachother). this will let you divide the staton using windows and expand by 1 block width to block access from center controls while having a beacon or antenna (or both) to allow others to find the station (set at max range) also having the station set to you as owner with share all set will allow everyone to use but not claim the station to keep it neutral. by dividing the station it will make it so person a can not go to person b ship from inside station.

Description coming soon. but basically this is an Automated Trade station. watch the video for more info.

you can also find the save file in your roaming appdata and replace the Thumb Picture with what you want. once you do this then publish your world. if you make changes and update your world make sure you replace the Thumb with the same image.

when in world before publishing.
press "ESC"
click "save"
click "yes"
press "ESC" 2x
click "exit to main menu"
click "no"
click "load world"
click "publish"

this will get you your thumbnail in the top right
once the world has been pulished got to your profile
workshop items
then find and select the world you just uploaded
on the right side you will see the part you can click to edit description, add photos, etc

How did you upload a preview image? The one in the top right corner and the image that serves as the main picture for the workshop entry?