Actually registering the drone is easy. It’s the other questions you have that bring up other concerns. Should I register as a hobby or commercial? What if I’m only going to fly commercial just once or twice? How does the FAA define commercial operations? What if I buy the drone from someone else, or want to sell a drone that’s registered to me?
In the two videos below I answer those questions.
How to register and what to do if you buy/sell a used drone
Commercial vs Hobby Registration