Congratulations, you are a certified open water diver! However, you don’t have to run out right away and purchase all new gear. Rental gear is safe. Rental gear also allows you to try different gear to get a feel for your personal preferences.
Purchasing used gear is safe if you know what you are getting. Make sure you test out used gear before you buy by having it looked over by a certified technician. Purchase used dive gear the same way you would purchase a used car. Inspect before you buy.