Heavy Support Squad Buildout - Imperial Fists

I plan on playing Imperial Fists. From the AoD box set, my initial plan was to build 10 as Heavy Bolter marines to shred through Infantry with the legion +1 bonus, and 10 Missile Launchers to give some coverage against Tanks or Troops. However, I was unsure if 10 Missle Launchers was overkill, or if I should go with just 5?

Thinking of also going for a Lascannon Contemptor for additional anti-tank support. But would I be missing out on the anti-tank support with this route?

Any thoughts or recommendations?