Hi, Mike.
Thanks for your interest in our plugin suite.
Event Aggregator (EA) would be the only purchase needed to bring in events from Google Calendar.
Note that if there’s a recurring event in Gcal, EA will import each instance of it as a separate event, not importing the entire recurrence series/rules. Therefore, having Events Calendar PRO (which gives the ability to create recurring events within WordPress) wouldn’t affect your import results from Gcal.
Last but not least, we have a pretty great Refund Policy so you can buy one or many of our add-ons and thoroughly test them.
I hope this info helps. Let me know if you have any follow-up questions.