Question Related to Watercolor Illustration

Photoshop is for working with pixel based images.  Illustrator produces math-based vector graphics.

Two different things with vastly different results.

It's not impossible to convert pixels to vectors. But it rarely works well with anything other than flat opaque artwork like gouache or acrylics with well-defined lines & sharp edges.  Painterly effects of watercolor washes & glazes would be nearly impossible to convert to vector. Also, depending on the complexity of your designs, Auto Trace may not be sufficient. You'll likely have to manually trace image paths, which can be very tedious & time-consuming.   EPS is a zombie file type. Most customers want editable .ai graphics or .svg for the web. 

For best results, use hot press, smooth finish paper for your artwork. Although I personally prefer to paint on cold press, rough textures don't reproduce well when scanned to digital output.

Use a high quality image scanner. Clean up as much as possible in Photoshop, removing artifacts, signatures and borders. Then export to high quality sRGB JPG.  See the Contributor User Guide for more details.   

• https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
• https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html
• https://helpx.adobe.com/stock/contributor/user-guide.html/stock/contributor/help/photography-illustrations.ug.html
• https://helpx.adobe.com/stock/contributor/help/how-to-submit-distinct-content.html
• Model/Property Releases:
  https://helpx.adobe.com/stock/contributor/help/model-release.html
  https://helpx.adobe.com/stock/contributor/help/property-release.html
  
  

Hope that helps.

Everything you need to,know about submitting assets to Adobe Stock is included in the help,pages:

https://helpx.adobe.com/support/stock-contributor.html

Yes, but you may have to include a property release stating that you are the owner and creator of the original design.

Please don't use image trace. You will have too many anchor points and messed up lines. it may look good to you but if you have to do any kind of edits, it will drive you crazy trying to find the correct anchor point and or broken line. You're better off tracing it manually in the program. It takes longer but its worth it in the end.