All hobbyist vapors should have an RDA even if its not the your primary device. But I agree with everyone else, with the new sub ohm tanks, you won't want to use your RDA as a primary as it can get a bit tedious with the rebuilding and easy leakage. (Check out these sub ohm tanks: Crown, Atlantis, Herekles). One of the benefits to having an RDA is the ability to change flavors at will; this is especially good for when you go to brick and mortar's to try out some of their flavors.
As for RDA's go, it's really a matter of preference. Here's a few things to look for:
• Obviously, the first thing you want to look at is the color and design to make sure it matches your mod and you like it

• Depending on the gauge of wire you use, make sure the posts have holes big enough to feed the wire through easily. My first RDA I couldn't fit lower than 28g in the center post (2 times for dual coil).
• Juice Well! I suggest you get something that has a big well so you don't leak easily and have space to easily but your coils and cotton without struggling. (I have very shaky hands so this was a concern for me).
Regarding your mod - if you're going to use an RDA, I suggest you get something that isn't a bottom button. Makes it super annoying to put down because you have to lock it and unlock it to use again. Also, I would suggest using a regulated mod over a mech. So many nice ones out (I personally use the sigelli 150) but that's another discussion in itself, but you may want to upgrade what you have now.
Just be careful with the RDA, make sure you learn how to build and how watts, ohms/coil resistance, etc. work together and read up on battery safety.
Good luck!