Wait wait wait, you have a Spartan in the list already? Perfect.
Command squad just improves the quality of the terminators as lot as they get WS5 and can issue/ accept challenges - which with a 2+/3++/5+++ makes them funny to tank things like enemy paragon blade preators while your own one minces a squad. Plus Fearless from the banner (massive in 30k).
Lascannons with Tank hunter are very strong, but I'd say you need a bunker and medic to keep them healthy.
Stone Gauntlet will indeed make your TDA & Breachers T5 as long as there is at least 3 models in the squad and they are in base to base, OR if you charge you get Hammer of Wrath, which is great too - but always take charges with breachers. BUT it imposes a limitation of you can't have more elites and fast attack than you have troops choices, so you'd need to be a touch careful. Command squads are HQ so that's another point for them too