Yes, windmill would likely be a great fit for that as long as you're willing to do a little bit of coding.

For instance, we do not have a calendar integration per se but can manage your oauth tokens towards any service (including gcalendar) and allow you to write code using their official sdks.

For spreadsheets, you can build a similar interface in windmill using aggrid.

It seems you also need approval steps and have your workflows wait for events, and that's built-in in our workflows.