For a beginner I would recommend a standard tube mechanical mod. Something copper has the highest efficiency. I use a Penny mod personally, but a four nine is a nice mod as well as a Vanilla or Anarchist. If you're a gun nut, there are authentic AR mods which are made from the barrel of an AR-15. You'll want an 18650 mod as the 26650 mods are massive. Also, make sure to buy a quality battery like an E-Fest 18650 or Sony VTC4 or VTC5 as they are safe to handle low ohm builds. Remember with batteries, if it has "fire" in the name, probably best not to use that battery for mods.
Now for the RDA, I would recommend something like the Tobh Atty (hence my name ;)) or I'm now using a DarkHorse. FastTech has many of these products available online for real cheap, but they ship from China and can take 6-8 weeks to arrive. Have a local shop do your first few builds and watch and learn.
Until you know what you're doing when building, DO NOT USE ANY OTHER KIND OF WIRE THAN KANTHAL! The risk of blowing your face off is real when you step into using nichrome or gplat wire. My current build is 6 wraps Royal wire, ohms out at about .06 which is the operational limit for the batteries I use.
I know this is a lot of info so if you have any questions, message me and I'll help you out. There's tons of videos on youtube for reviews and educational videos. I've been vaping over a year now and doing my own builds just as long. Can be a really fun hobby and using some 0 nicotine juice, you can enter into "cloud comps" and fog the hell out of a store, which is hella fun.
One Love,
tobh