I'm all for converted guard armies. I've done a few in my time and in my experience they have the most scope for conversions.
My only suggestion, is that while converted armies are cool, just try and makes sure that the look like they belong in the
40k universe.
For example, lascannons are pretty iconic looking, and as such the model you're using to represent one should always look vaguely like a regular lascannon. Just with your own personal spin on it ya know?
Also, if using historical kits for your vehicles try and "grimdark" them up. So chunky armour plates, rivets and thick tires etc.
You want your opponent to still feel like they're playing a
40k game, not a historical re-creation.
That said, this sounds like a great idea for an army and I can't wait to see some completed models
Dave