I agree about Priests, they are a must. I'd also drop the Death Co as they are costing probably two Assault Squads in total roughly.
If you want re-roll to hit then a Librarian is better as can use unleash rage in both yours and in the opponents assault turns, plus can have shield which gives your dudes a 5+ cover save on the way to the fight.
You also need some long range anti tank to supress units and pop tanks before your Assault Marines reach the enemies lines and cut down numbers. I'd take triple 5 man
Devs with full house of missile launchers.
So I'd do this:
Librarian - jump pack, shield of sanguinus & unleash rage
Librarian - jump pack, shield of sanguinus & unleash rage
Honour Guard - jump packs & 4 x plasma guns
3 x Sanguinary Priests - jump packs
Chaplain - jump pack
Chaplain - jump pack
10 x Assault Marines - 2 x meltaguns - sgt w/ power fist
10 x Assault Marines - 2 x meltaguns - sgt w/ power fist
10 x Assault Marines - 2 x meltaguns - sgt w/ power fist
10 x Assault Marines - 2 x flamers - sgt w/ power weapon
10 x Assault Marines - 2 x flamers - sgt w/ power weapon
5 x Scouts - sniper rifles & camo cloaks
5 x Devastators - 4 x missile launchers
5 x Devastators - 4 x missile launchers
5 x Devastators - 4 x missile launchers
Check points because I haven't. You've got a better
HQ choice with more benefits, Priest plus one from the Honour Guard who dish out plasma death, still got the Chaplains, some flamer death, cheap objective holding unit and lastly some ranged supression units