It depends on what you are trying to do. If you are just over dimensioning hardware so you can be sure you do not have to worry about performance then go ahead and do not worry about performance.
If you are doing this because you have a genuine concern about performance than you need to do some reading up on Postgres performance tuning. The Postgres defaults are not optimal for production environments. A simple Google search for “Postgres performance tuning” or something along those lines will yield enough useful results.
Also, this may or may not be obvious but you need to properly think about monitoring, backups, governance and whatever else comes along with hosting an application.