You asked a lot of questions, and I'll try to answer most of them.
The different
clearomizers have minor differences in how they are built and the differences between each one will be minimal. Clearomizers in general will mute some flavors. The clearos that are top coiled also have their string wicks located at the top of the tanks, and will need frequent tipping or swirling of the tanks to keep the strings wet to prevent dry hits. The bottom coil/bottom wicked clearos have gravity in their favor, so this is not required.
The Vivi Nova and iClear 16 & 30 are top coiled, so they might provide a warmer vape and as they are filled from the top are easier to fill. the Evod and Protanks are bottom coiled, so they might provide a cooler vape and they are filled from the bottom. This requires that they be removed from the battery and turned upside down to fill.
The iClear 16 & 30 are dual coiled, meaning they have two heating coils, which may allow them to make more vapor and throat hit.
The Evod and iClear 16 are strictly ego threaded, so to use on a 510 battery device (like most mods are), they will need an adaptor to use them.
_____
Concerning
coil resistance (ohms), lower numbers means a warmer vape (hotter coil). Higher numbers mean a cooler vape. That's all you need to know at this point.
_____
A single/
fixed voltage battery will perform best at its fullest charge; after that its all down hill as the battery becomes drained during use. Vapor will gradually decrease as the charge weakens.
Variable voltage is regulated voltage by a mini-computer. You set the desired voltage, and the computer makes adjustments to keep the voltage to the coil to stay the same despite the battery losing its voltage as you vape. You can also adjust the voltage for a "stronger" hit by increasing the voltage. You can adjust the voltage higher or lower depending upon each individual flavor you use (they all have their "sweet spot" voltage where their flavor is best). All of this regulation takes a slightly higher toll on the battery if you use higher voltage.
_____
I've written a series of
10 blog articles that you should save for future reference reading.
E-Cigarette Forum - Baditude - Blogs
For your future battery device, I recommend one of the following. Both have variable voltage. Both are small and pocket-friendly for both home and out-of-the-house use. One is tube shaped and the other box shaped. Both are extremely popular for novice, intermediate, and advanced vapors.
Innokin iTaste MVP
Vision Spinner ego battery