Whether you should apply for a patent in other countries depends on the exact facts of your situation. It’s a long and expensive process, and the patent is of little value if you don’t intend to sell your product or service in that country, or at least enforce your rights there.
One of the best times to consider filing a foreign application is about eight months after you file your domestic application. There is a deadline of making the foreign filing within twelve months from the initial US application for most foreign countries, so the eight month mark gives you time to consider your options.
Revisiting the idea of a foreign filing at eight months also would allow you to include improvements made since filing in the foreign applications, or Patent Cooperation Treaty (PCT) Application.