URL length does not have much impact on how Googlebot crawls.
Changing your URLs will have the biggest effect. Googlebot will forever come back and crawl your old URLs. You will need to implement redirects to the new URLs and maintain those redirects indefinitely. If you change all your URLs, this can significantly increase the number of URLs that ...
No, it won't.
All you need to focus on is to make things easier for the end-user.
Everything else doesn't matter anymore.
Google's algorithms are very evolved and what's good for the user is good for robots and ultimately for rankings.