Tank: I don't see the coils from the EVOD going away any time soon. So you can hold off on getting a new tank for a while, IMHO. You just need a 510-to-Ego adapter.
Mod: If you want something small and simple to use with a built-in battery, is small and light, then I suggest you look into an
Eleaf Istick 30W. That full kit I linked to comes with a 510 to Ego adapter so you can use your evods on it without buying the adapters separately.
As far as VW/VV mods go, it's as simple as it gets compared to today's mods that have a bunch of settings which can be confusing if you're not used to it. Just set your wattage and vape.
The istick 30W has both VW and VV mode so you can choose whichever you want by simply clicking the fire button 3 times to toggle between the two modes.
You can press the up/down buttons together for 2 seconds to lock the device to it's current voltage/wattage sting so you don't mistakenly change the wattage/voltage of you accidentally bump the up/down buttons. Do the same to unlock it.
No other settings. 3-buttons - 2 for up/down wattage/voltage adjustment and then the fire/power button.
Easy peazy.
I just looked in the Istick 30W manual and I don't see where it says you can vape while charging, but I think you can. But honestly, I don't recommend it. I recommend you just get 2 mods and make sure you keep one charged while vape on the other. If one breaks on you then at least you have another. But I can tell you, the mods do last. But if you vape while charging, it may shorten the life of the mod and could damage the USB port. I just don't recommend vaping while charging.
I know you need to save money, but 2 mods is really better than one mod doing vape-while-charging.
They are a good mod for your purpose. You may be able to find them cheaper, but just be careful as they are a highly cloned mod.
If you buy from Fasttech, just make sure whatever color you choose that it says "US plug adapter" as those are the full kits. All others are just the mod and you won't get the Ego adapter, wall adapter or charge cable.
EDIT: Don't bother to get the istick 20W as it's not worth it for many reasons. The 30W is built better.
EDIT 2: If you go with another mod, make sure you look at what the lowest wattage is that it will do. There are mods out there today that might not go as low you you like to vape. Since I don't know what wattage you vape at, I thought this was something worth noting.
Edit 3: If you go with another mod, since you'll need a 510 to ego adapter,
I recommend these over
these. They are the same ones that come with the Istick 30W kits and are easier to screw on and off your eGo clearomizers due to the wider, knurled base.