[SimulatedSnowman]

Definitely spend the points and get yourself either a Heroic Senior officer or an Honorifica Imperialis on your commander. You're seriously gonna want that leadership. Multi-lasers are a good all around choice, but like qsd said, Autocannons have longer range and strength. Really it's a matter of flavor, since either is nice.

Your infantry wants heavy/special weapons. At least heavy weapons. A line Infantry squad without at least heavy bolter is like... it's like... I don't know what it's like. It's not in my realm of understanding. You have enough anti-tank weapons, and I'm assuming that you want your hellhounds to do the majority of your anti-horde, but I'll tell you from experience that Hellhounds draw a lot of fire. It would be useful to have your infantry be able to give a little more oomph to their horde clearing.

Adding Heavy Bolter Sponsons is a good idea for two reasons. 1, even though as you said it's a 1 in 6 chance, if you take that 1 in 6, your tank is useless for the game. So technically, there's a 2 in 6 chance your tank is rendered ineffective, one being you lose your battlecannon, two being your tank gets destroyed, and on a penetrating hit, those odds get worse. 2, there are definitely situations when it is more prudent to shoot 9 heavy bolter shots than to scatter a pie plate, such as if you're moving your tank and don't want to take the 2d6 scatter for it. It doesn't cost all that much to upgrade, and the rewards are well worth it.

The Demolisher with a Lascannon is also a little iffy. The fact of the matter is, Demolishers are good up close and dirty. If you're keeping your Demolisher back to fire its lascannon, you're denying its real strength. I would suggest that you take heavy bolters all around again, and maybe take smoke launchers. This way you can roll up, pop smoke and be relatively safe for your opponent's turn, then drop the serious stuff on them on your turn.