Hello Rich,
Super question you have there!
Unfortunately it is not possible to limit the number or words with the shortcode.
You might be able to do that with a template override, which would also override the original photo view as well.
To get started I recommend these 2 articles:
https://theeventscalendar.com/knowledgebase/themers-guide/
https://theeventscalendar.com/knowledgebase/template-overview/
Once you read through those, you will need to create an override for this file:
wp-content\plugins\events-calendar-pro\src\views\pro\photo\single-event.php
and copy it to:
wp-content/[your-theme]/tribe-events/pro/photo/single_event.php
You will need to modify line 52, which says:
<?php echo tribe_events_get_the_excerpt() ?>
One other solution might be running tribe_events_get_the_excerpt through a filter.
I hope this helps, let me know.
Cheers,
Andras