Online transaction calculations

Questions
1

I am trying to map out how I want to build an app that users can book and purchase online services from vendors using a calendar and filtered search.

My questions are:

  1. for online booking using a calendar (vendor would have calendar on their page) should I use google calendar (assuming this can be done, right?)?

  2. The vendors will have services that vary in cost depending on what services the end user selects. Are math calculations done in Bubble or through and API, and what API if necessary?

Thanks guys and gals for the help and thoughts!