Hey mate, new to the game as well or just the guard?
A ccs is solid, with it bare bones like yours it will be focussed on giving orders. consider giving them the autocannon though, since they are BS4 and will hit more reliably.
The very light pl you have there is good, but it will fold to anything if you try and use each element independently. They are weak when separate, but keep them concentrated and close to your commans squads for orders and they will perform much better. make sure you read up on orders tactics too! all in all a solid choice for defending your nearest objective.
These guys are your rockstars. they will wreck marines up to 12" with the plasma and chimera shots, but ideally you'll be either racing them to hold mid to distant objectives or mop up the remainders after your tank shoots. Without grenadiers, stay mounted or make sure you use the tank for cover.
Vanquisher battle tank
This is not an option i would take at 500 points. Bs3 means a 50/50 chance to hit one model (twice including the lascannon) and although you will have no difficulty penetrating armour, you have nothing to offer versus infantry blobs, squads or monsterous creatures that the equivalent points in HWT can't do better. I suggest swapping this for a Leman Russ Battle Tank with Heavy Bolter for general support vs infantry and vehicles, or a demolisher to frighten everyone silly and draw fire. if it lives, and it should at av14, It will dish out major pain once it gets to 24".
Interested to hear your thoughts.