If you do get an eGo, I would def get a regular one and use cartos instead of getting an eGo-T. The tanks can be very finicky and leak a lot. They also dull flavor and TH, even when their working correctly. If you want to use a tank, your much better off getting a carto tank. They give a lot better vape than the eGo tanks, and are a lot more consistant too.
The Smoktech 3.5ml tank is perfect for eGo/kGo/E-Power sized PVs. Smoktech does make a bigger 6ml tank, but personally I think they look funny, and they make the PV really top-heavy. The 3.5ml tank is perfect size and doesnt make the PV top-heavy. The Smoktech tanks are dual coil tanks, but that doesnt mean you have to use dual coil cartos in it. Personally I think dual coil cartos suck on lower voltage PVs, and they only really shine when used in the 4-5V range. The Smoktech tanks are really cheap and you can get a 3.5ml tank for about $10, and it comes with a pre-punched DC carto in it and a drip tip, which makes it an even better deal. Like I said before, I think dual coil cartos suck at lower voltages so I didnt even use the carto that comes with the tank. Instead I use the Ressurector cartos in the tank and they work a LOT better than any dual coil does. They are single coil, but are the same size as a dual coil carto so they fit perfectly in the Smoktech dual coil tanks.
Crystal Clear Vaping sells the Smoktech tanks, and they also sell pre-punched Ressurector cartos for the tanks, and they have the metal base on them like the DC carto that comes with the tank. You dont necessarily have to use a carto with the metal base, but they are nice bc they stop the tank from being able to slide down.
This is what the Smoktech 3.5ml tank with a Ressurector in it looks like on my E-Power:

The tank is big enough that I can fill it in the morning and easily be good all day, yet its still small enough that I can easily carry it in my pocket.
I think the Smoktech 3.5ml tank with the Ressurector cartos is a perfect tank set-up for the E-Power, kGo, Riva, and even eGo (even though the Ressurectors dont run at full potential on an eGo), and is def better than using the eGo-T tanks