Well, first of all, doctrine queries are best suited for the
40k fluff part of the forum where you'll find all the history boffs.
Your post is pretty vague about what you're looking to do, so I'll try to be as broad as possible.
1) Abaddon is a special character in Codex : Chaos Space Marines and the Sons of Horus, Horus Heresy: Betrayal heresy era legion list. He could by all means be a 'counts as' Captain in Codex Space Marines.
2)Justaerin Terminators are a seperate elites choice you can take in a
HH:B legion list, and Abaddon only affects them by allowing his squad of Justaerin to deepstrike, which usually isn't an option.
Terminators in C:
SM have a single power sword for the Sergeant and power fists for everyone else. Hence, you'll need to outfit your Justaerin this way if you want to field them using C:
SM rules. It is also worth noting that you *cannot* take a multi-melta in a C:
SM Terminator Squad, or indeed any Terminator Squad outside of the
HH:B's Justaerin.
Codex: Space Wolves would be something to consider - their Terminators can take power weapons as default, letting you go all power axes without any conversion work bar the
MM.
3) You cannot mix and match rules from different Codex's - troops from
HH:B's legion list cannot be used with C:
SM. You can do 'counts as' Tactical Marines freely, but you won't be getting your heresy era 20 man squads unless you use the Chaos Space Marines Codex.
4) Just off the top of my own head, the motto of the Sons of Horus is the idea that you have a 'tip of the spear' that plunges into the heart of the enemy. Terminators would typically assume this role, so one or two squads of them would be fairly fluffy. I'm not 100% sure but I believe Horus also used assault marines in this role.
Finally, if you haven't seen it already,
FW released some new models today, including some SOH stuff:
http://www.forgeworld.co.uk/New_Stuff