Sorry, but you are asking too many questions for me to help out.
I am not familiar with “the WordPress calendar”
As for the “map their coordinates in the Google Map “, this is something you can read about on the ACF google map documentation page.
I am not familiar with the Geo Mashup plugin and can’t provide support for this compatibility.
I think you need to break up your task into small achievable milestones and then ask specific questions to the relevant developer. For instance, I can help you with any ACF related code, but if you are using a calendar plugin, you will need to ask them how you can modify the query to use a custom field as the sort order.
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