Even if the Windy API key were smaller you still would not be able to upload to Windy with your Ecowitt console using the "Customized" server upload feature because it uploads using a different protocol than what Windy uses.
My suggestion for you is to use the Ecowitt GW1000 or Froggit DP1500 in conjunction with your station if you don't currently have one of these. It will be compatible with your current station as long as you get it with the same frequency as your current station (433, 868, or 915 MHz).
Then you can run one of the follow software applications that are capable of getting data from the GW1000 / DP1500 and uploading it to Windy. These compatible applications are: Cumulus MX, Meteobridge, Weather-Display, and WeeWX. A good solution to run these is a Raspberry Pi. If you need more guidance you should head over the wxforum.net and read up on these solutions or ask for help there.