Is there a way to contribute several images as a set?

If these are vector graphic icons, as an example, you can submit an icon set as an Adobe Illustrator file (.ai).

• https://helpx.adobe.com/stock/contributor/help/vector-requirements.html
  
  

Hope that helps.

What type of assets?

• Photographs,
• Hand drawn illustrations,
• Vector graphics,
• AI Generated,
• Other...

Similar images will be automatically suggested to the Buyer when they view one of them. 

No. The system will detect that the images are the same model (model release) and may also be that they are similar. Be sure not to spam the system. Normally, you are allowed to submit 3 variants of a certain setting.