Well, first things first, welcome to heresy.
Now onto the list. Maybe something like this....
Captain w/ artificier aromour and relic blade
Tactical Squad (10 man) w/ flamer and missile launcher in rhino
Tactical Squad (10 man) w/ melta and missile launcher in razorback w/ lascannon and twin linked plasma gun
Sargent w/ power weapon
Scout squad (5 man) w/ ccw+bp and teleport homer
Terminator squad (5man)
Assault squad (5man)
Adding the captain to 5 marines (sergeant + melta + 3 bolters) in the razor back for assaulting objectives with the other 5 marines (missile launcher + 4 bolters) to guard an objective. Whilst the scouts infiltrate and allow the terminators to deep strike in to kill any tough opponents. Use assault marines to kill any squishy non close combat units (such as guardsmen or devestators).
however a more optimum build would be dropping the scouts, terminators and assault squads and replace them with a pair or auto las predators but seeing as you dont yet have them the above list would be an ok choice.
Hope any of this has been of at least some use.