will be building a rack to save on some money

Im using a rack design from the DIY section. the shelves will be 2ft Wide by 4ft Long..

This is all new to me, so Im unsure of what size of heat tape to use?

22" at 17 watts/ft. = 12 3/8" panel.
11" at 20 watts/ft. = 12 3/8" panel.
4" at 8 watts/ft.
3" at 10 watts/ft.
3" at 6 watts/ft

will be ordering a Helix thermostat along with the flex what from Helix

thanks