Before you jump in to the deep end, allow me to shed some light on a couple of things here.
First, the mod. ------- There are many types and they come at many prices, but what exactly are they? Well, at the most basic level, a mod is nothing more than a flashlight. It's a battery in a tube with a threaded top so you can screw in a coil. They work exactly like flashlights in many ways.
Now, in regards to ecigs, there are two basic types of mods. You've got your Variable Voltage/Variable Wattage mods and Mechanical Mods.
Again, these are basically the same thing. The only difference between them is the Variable mods have an electronics pack inside that allows you to make changes to the power output and to provide certain safety features. Mechanical mods on the other hand are literally like standard flashlights with no electronics inside and a simple mechanical button to make it fire. Because a mech mod has no electronics or safety devices built in they are capable of delivering a LOT more power to the coil than a VV/VW mod. Also, since the mech mod has no electronics or safety devices it's a LOT easier to damage your batteries or worse.....
So, which is right for you? That's a lot of personal preference.
Personally I find the Variable Voltage/Variable Wattage mods too "fiddly". To really get any benefit from these mods you have to adjust the voltage, and adjust the voltage frequently. If you're the type of person who wants to tweak your voltage settings to bring out certain aspects of your juices, and use different settings for different juices than a VV/VW mod is just what you need.
If you're the kind of person who would prefer to have a single setting and then just leave it alone and vape then I would not suggest a VV/VW mod. It's a waste of money for that type of use. It's too limiting. For the same money as that SVD you can get a high quality mech mod and a Kick unit and do virtually everything the SVD can do and several things it cannot do. You'll lose the ability to adjust voltage, and you won't have an inaccurate ohm reader built in, but you can subohm and vape at wattages that the SVD simply cannot touch.
Now, I mentioned the Kick module, so obviously a bit of explanation is in order about that. A Kick is a little round electronic device that fits inside the mechanical mod between the positive battery terminal and the top contact pin. There is a small dial which allows you to adjust the wattage setting. You decide what wattage you like, set the Kick, and that's all. You can change coils and toppers all you want and the Kick will provide the same wattage to the coil every time. It also acts as a safety device so if there is a problem it will simply not fire rather than allow the battery to be damaged.
If you reach the point where you want to subohm or pull wattage and amp draws that exceed the limits of the Kick, you can simply take it out in a few seconds and then you're free to do what you want.
There is often a HUGE difference between the size of a VV/VW mod and a mechanical mod. Those electronics tend to make the VV/VW mods much larger which leads to some misunderstanding. We're often led to believe that bigger is better, but in mods the bigger is the lower powered and more limited VV/VW mods while the more powerful and more versatile mech mods are significantly smaller.
You wouldn't think it, but the little bitty mech mod on the left can deliver more power than that huge SVD on the right...
If you are EVER going to consider subohming then a VV/VW mod is a waste of money. Quite simply, they cannot do it. (A few can, but those very few come with an astronomical price) You'll be far better off starting with a mech mod with a Kick and then remove the Kick when you're ready to start subohming.
Now, as far as RDA/RBAs go, I would highly recommend starting cheap and easy here.
Before running out and getting that Kayfun that everyone talks about, get something like the IGO-W or Trident clone to learn on. It's a $20-$30 investment that will allow you to easily practice your coil building with. You can try different coil types and different ohm coils and switch them out quickly and easily. Once you are comfortable building coils and have a good idea of what you like, THEN start looking at the more high dollar RBAs. By then you'll have a much better idea of what you are doing and also what you want from your next device.
Knowing what you want will keep you from wasting money on things that people say are great, but don't provide what you want. People will always recommend what works great for them, but that doesn't mean it's going to work great for you. You need to give some serious consideration to what exactly you want before spending more money, because I can assure you the mod path can get really expensive really fast if you're buying without knowing if your purchase will satisfy your desire.