It should not be capitalized, but the slash is always present. Names of alien species, including the Human race, are always capitalized. Astronomical unit, caps, not lc, and no periods.
Antimatter is the preferred term.
Other, larger numbers have been used, but are rare. Singular and plural forms are the same. When referring to mankind. This is done to match Zhodani, Solomani, Vilani, and so on. Likewise, always capitalize the word Human in Traveller.