If you're starting with an RDA I'd suggest some research into what you want and what you can do as far as airflow. Using an RDA requires good airflow or you're going to get a very harsh hit. Do you want one that has adjustable airflow or are you okay with drilling it out yourself?
Before you start buying any supplies, make sure the first thing on your list is a dedicated ohm meter. That's very important to make sure you're safe. Do not rely on an APV to read ohms of a coil correctly and accurately.
Next is the wire. 28, 30 and 32 gauge A-1 Kanthal is a good start.
Organic cotton is a popular choice for wicking material.
High VG juice with lower nic level is also another thing you'll need. For example I regularly use 12 mg nic at 50/50 when I direct drip with an atomizer and also use in my tanks. In my RDA I use 3 or 6 mg nic, 20PG/80VG. If I don't drop the nic and increase VG, it feels like my throat's getting ripped out and I get way too much nic at one time.
Other things you may need are tweezers with insulated grips, drill bits or a Qcoiler to wrap your coils, good eyes, nimble fingers and lots of patience. A good mini torch is very handy but not entirely necessary.
Good luck!