Hi, in my area which is Boca Raton, FL the major airport is a Class D called "Boca Raton Airport". Every airport has their own procedures on how to contact them for UAV notification. The procedures are usually posted to their website, for example, the one near my home (within 3 miles) has the following instructions:
Drone Notification Procedures. The one in Tampa, FL has a nice form you can fill out.
There are also two other helipads near my home, one for a major hospital and another I believe is a corporate helipad. In the B4UFLY app, the phone numbers listed for those two helipads is the same number listed for the Boca Raton Airport. So in my case, I just follow the posted procedures and that satisfies my requirements to fly as a hobbyist within 5 miles of the airport and the helipads. You should check the numbers listed in the FAA B4UFLY app. Note that this app allows you to submit a form but it is currently only a test and does not satisfy the notification requirement...you will need to call. If no one answers, leave a message. Some people say leaving a message satisfy notifying them but for me it's not enough...I have to speak with someone or I won't fly, but that's my personal choice. In my case, I try to schedule my flights to when I know someone will be able to answer the phone.
The 333 requirement and COA is needed if you are planning on flying for business. First, you would need to get the 333 exemption to get a blanket "permission" to fly at distances greater than 5 miles from an airport, then you need to apply for a COA to be able to do commercial flying within 5 miles of the airport. The COA is specific to the airport, if you have many, then you will need to submit one per airport. Then to be able to fly your commercial missions, you would need to hold a Sports Pilot Airman Certificate at a minimum. You would also need to post a NOTAM at least 24 hours before the mission and remain in contact with the tower and have a spotter.
It is very complicated and asinine that as a commercial operator you have all this red tape but as a hobbyist, all you need to do is contact the tower and that's it.