EDIT: worked figures.
If you've settled on 16 cells, let's work some numbers.
Using a realistic figure for an 18650 cell (3400mAh) we get 219Wh for a 16-cell pack.
which works out to 43.8 Ah @ 5V for the pack
Weight for the batteries alone: 720g (45g/cell)
16 cells is double the size of a large laptop battery. At 5V @ 2A this battery will take about 20-30 ...
To prevent condensation the components in the cabinet should be above the dew point.
There are two ways to do that:
Reduce the relative humidity, for example with silica gel.
Increase the temperature, with a heater.
When cold the chemistry in the battery slows down. Which increases the internal resistance of the battery, reducing it's effective ...