You'll find out when you hit an API limit when the app stops loading data properly. You can get a sense of how many API calls are being made by running a Monitor session while using your app.
You are right in that many data operations generate an API call. If functions such as LookUp(), Filter(), Search(), Collect() and connectors query something other than an internal collection, you are almost certainly making an API call. Your app will become more responsive the more you minimize these external data queries.
Hope that helps,
_________________________________________________________________________________________ Help the community help more users by choosing to "Accept as Solution" if this post met your needs. If you liked the post and want to show some appreciation, please give it a Thumbs Up.