Again great feedback here and in the other forums!
Thanks allot mates 
Now that most decisions are done, the basic skeleton build complete, I was able to look at the actual "beefing up" and adding armor.
For this I wanted to keep the 3-sided (or 6-corner) approach that I also used on the carapace.
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The first section of armor plates on the thigh of POLLUX.
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And on both walkers (they now look a bit like Dutch Ice Skaters
)
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The first armor plates for the shins.
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Here you can see clearly the difference with and without shin armor.
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While the Green Putty cured I added a shield to CASTOR.
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The putty sanded and cleaned up.
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As a final detail I added a plastic card ornament to the shield.
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And then it was time for rivets - plenty of rivets 
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And POLLUX with rivets - did I tell you how much I like his pose?
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No, I LOVE the pose 
POLLUX and CASTOR completed!
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So, what do you think?
Do they look Imperial enough?
Now I will start to look into the other combatants and the actual construction of the street and buildings. So I will browse the Hirst Arts gallery (http://www.hirstarts.com/projects.html) for some inspiration.
As opposing combatants we'll have some Orks. I have the idea of an Ork emerging from a sewer manhole and firing an RPG-style rocket launcher, but I still need a bigger opponent, worthy of POLLUX or CASTOR.
Maybe a tank or a emplaced gun (no walker, as I've already done some Ork walkers
)
I look forward to your C&C and suggestions.
Cheers
Klaus