Detailed Ground Combat

[Suicide Junkie]

Kt Size has no problem being zero.
Except for the fact that it may allow designs with an infinite number of components. (Use the X-per-Vehicle restriction, or a high cost to dissuade players from adding too many)

Hitpoints being zero is a problem, but only if the whole unit can be designed so as to have zero hitpoints total. Be sure that at least one of your required components has a hitpoint.