Peter, there's just a small hole in your Imperial Guard strategy: they have a BS 3. Yes, I'm afraid our friends, the Imperial Guardsmen, are not known for their marksmanship. And, it transfers over to their vehicles. If you're firing any vehicle other than a Leman Russ or a Bassie, you have to roll to hit. And you will miss my friend, many many times. So yes, while you should be able to roll across the board in your chimeras, and let loose with the multilasers, lasguns and other various forms of death, chances are you'll miss about a third of your to hit dice, just cause you need a four or higher to merely hit. Then, you'll probably miss another third, or even half of the ones you have left over since pretty much everything out their has a higher toughness than the lasgun's strength. So, with a ten man guardsman squad firing at a 10 man marine squad, you'll be lucky to wound three of them, and then of course, there's that pesky armor save. So, all told, it's a champagne-worthy moment if you kill two of the three you wounded, but most likely they'll either make all of the saves, or you'll kill one. Forget about assaulting, lasguns are rapid fire, so your squad will get raped next turn by 9 extremely pissed marines.
A few more points: the range on a Demolisher's main gun is 24", it is not a sit and shoot weapon. And since vehicles can't move and fire an ordnance weapon, your rolling death tank scheme for the leman is slightly flawed as well. Also, you do realize that basilisk shots are ordnance, and that scatters? You would have to roll a hit on the scatter dice in order to kill the command squad outright, plus most commanders have Invulnerable saves.