Classic Grid thumbnail height

AND/OR how can I set the excerpt length? because if the image is tall, I could have more text show...

see example here, and why I'd like to reduce the height of the thumbnails

https://www.autocrosscarballo.com/

Hello 

How can I set the height for the thumbnails in the Classic Grid view?

You can change image height in the "Styles and Layout" section. See screenshot.

In the blog layout, you can try to change the "image size" option. In some cases, it may help.

AND/OR how can I set the excerpt length? because if the image is tall, I could have more text show...

It is not possible in an easy way. You have to override the plugin template file (templates/teaser/classic.php) and set a bigger number of words in code.