Howdy,
I'm busy with a similar project.
Don't think there are KT21 rules for Eliminators, Supressors, or Terminators (yet), but I could be mistaken? There is also Deathwatch, but guess those are the veterans you listed.
Most Space Marine KTs have 1 Sergeant plus 5 Warriors; however, Heavy Intercessors have one less Warrior, and Scouts have four additional slots.
Tactical Marines, Scouts, and Deathwatch Veterans have extra roles too, such as Gunner, Heavy Gunner, etc.
I opted for a box of Reivers to learn the rules with--they were on sale and I like the skull helms and carbines
Good luck with the project