Carto tanks are nice There Are many to choose from. You don't need anything else bc the tank is basically just a juice reservoir for the carto and you still screw the carto on like you normally would. I don't see why you'd ever need a feeer system for a tank, because a carto tank basically does the same thing that a feeder system does, just in a different way. Instead of squeezing a bottle like you would on a bottom feeder to feed more juice to the carto, a carto tank automatically feeds juice to the carto through a punched hole or holes in the carto. You wouldn't need a feeder system bc if you want to hold more juice, you can always just get a bigger tank.
If you do get a 5V box mod and a smoktech tank, I wouldn't use the carto that comes with it bc it's a 1.5ohm dual coil. That's low for a 5V PV and will prob burn the juice. You can just replace it with an XL carto of your choice.
I use the 3.5ml smoktech tank on a 3.7V Epower, and even though the 3.5ml is the smaller of the Smoktech tanks, a full tank still easily lasts me a full day without needing a refill, and personally I prefer the smaller tanks bc the bigger ones look funny And are topheavy on the Epower or similar size PVs.
Your welcome to get as big of a tank as you'd like, as long as your okay with how a big tank looks on a fairly small box mod. The 6.5ml Smoktech tank would prob be able to last you a couple days before needing a refill, depending on how much you vape
