Look at the image below and follow it exactly. Feel free to tweak to your needs.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3422334428

In summary:
Max Buy = how far you want Supply ships to look for wares
Max Sell = How Far from 'Trader Home' do you want Supply ships to sell wares
Wares: ONLY SELECT THE WARES YOU WANT TRADED
Trade Bans: Bans all trades except for the player.

Best of luck!