Here is my use case. I need to consume 'account activities' data from an external system and just display in Salesforce when requested by the user and not persist the data in Salesforce. For this I thought of using Salesforce Connect. The team that supports the external API then came back to me saying that they will not be able to support Odata2.0 or Odata4.0 and they could only expose the external service as a REST service. Hence I went the route of developing a custom apex adapter and consuming the external service into Salesforce using Salesforce Connect. I referred below aricle for the same.

https://www.jitendrazaa.com/blog/salesforce/implementing-custom-apex-adapter-for-salesforce-connect/

From what I have read , the call out from the custom apex adapter needs to be a Synchronous call out.

My question - If the external service takes more than 5 seconds to send me a response (for whatever imaginable reasons) , 
1) Am I at risk for hitting the 'Number of synchronous concurrent transactions for long-running transactions that last longer than 5 seconds for each org' governor limit when I have around 800 salesforce users and the account activities external object added as a related list to an Account?
2) Is there a way to get around this governor limit? I will not be building any custom lightning components as the related list for the external object would become available out of the box from Salesforce.