[Fyron]

What is the lowest amount one can use for tonnage/space of a component? Is it atleast 1? Can I put in say, 0.5 or 0.2?

You can multiply the size of all ships and components by 10, then use single digit numbers as fractions to get the exact same effect. You can have ships up to ~65000 kT, which should be more than enough if you aren't making the ships be bigger than 6500 kT already. Since the SE4 kT is a completely arbitrary unit with no bearing on reality, the change in scale doesn't really matter.