Watch some reviews. DJlsb Vapes, Mike Vapes, Rip Trippers (over the top but knowledgeable), Grim Green, VapinFagan, to mention a few. For the most part the RDA you choose will depict how many coils to use. RDA's will work fine on your Alien. RDA's are also a great place to start building as they are very easy to wick. RTA's are finicky and take practice. Get familiar with this site: http://www.steam-engine.org/coil.html It will help you design a coil. The RDA itself will also have a lot to do with what build you use per the amount of space on the build deck. Do a little research on Battery Mouch. He is da-man when it comes to choosing good batteries for a mod. 18650 batteries are not spec'd honestly by most manufacturers. It is good advice to understand ohm's law to understand how the resistance of your coils effect the mod. The relationship between wattage, voltage, amperage, and resistance is also good to understand.
There's a lot to learn if you so choose. Vaping can be a great hobby and as intricate or simple as you want to make it.