Yes, he is not a unique character. I don't see a good reason to do that though, what are you planning to do? Run an Eternal Starhost but have an extra Warden for your Slann?
Yes. Sadly in yesterday's game the Warden was killed early on and the Slann fell victim to 30 archers!
Also, does the Starhost count as a 'unit' when you cast Mystic Shield, or does this spell only cover one of the three units that make up the Starhost?