[experiment 626]

a) swap the storm trooper doctrine for hardened vets as they're godly for guard... 3 special weapon slots + power fist option for the sergeant and the ability to mix and match basic weapons! (i love my shotguns!)

b) drop mechanised as you don't need it for any reason; every unit you've taken already has the option for a chimera.

c) grab up iron discipline and turn your officer into a heroic senior officer for the all-important Ld9. think about adding in a vet w/company banner too as those re-rolls can be real life savers!

d) i'd drop 1 hellhound and take 2 single sentinel squads. (1 as your 3rd FA slot & 1 as part of your command platoon)
autocannons rule! they are the best weapon in the game for tackling skimmers, which is a big weakness for you right now.

e) switch-up the weapons a bit on your chimeras. IA gives you the option for a turret autocannon, while going all heavy bolters will help against anything not in power armour.
a heavy flamer or two will also discourage hoards and can be used in a pinch to reach out and nab any tau/eldar 'fish of fury' formations.

f) if the grenadiers are going to tank-hunt, then i'd drop them down to only 6 men without a vet sergeant. leave the hardened vets to fill the role of 10-man 'front line' squads as they can take that 3rd plasma gun + are better in assaults.
this will save you some pts for getting smokes & extra armour for all your vehicles + add on some pintle-stubbers for those veteran transports! (you really can't say no to 9 shots/turn!)

hope this helps,
cheers!