Hi,
Like every major release, it's better to run the update on a copy of the website first just to make sure that the main things are still working.
Normally, the 3.5.0 and the 3.5.1 mainly bring fixes and a new address edition on the checkout. If you didn't customize the view files relative to the address system in the checkout, you should be pretty good for the update. Otherwise, you'll have to remove the customization in these view files and reapply your changes to the new version of these views after the update.