Happy to hear that the Writing Efficient Filters article has been helpful for you!
Yes, the concepts in the article around efficiency also apply to FINDROW() and FINDLASTROW(). These formulas both work similar to filter formulas; The difference being that FINDROW() returns the first row of the specified criteria, while FINDLASTROW() returns the last row.
For your last question, the guidance in the article you've noted will help with overall performance of your app. Also, setting up data models with clear data relationships will allow for simpler formulas and app structures to more easily create and run apps.