Hmmm, as far as I know an Elf will not lose power when he is rehoused. After all, death is not something an elf is supposed to experience, though the Marring of Arda and Morgoth evil works are responsible for the death of many Elves and the fading of their hroa. Therefore I believe that Elves will stay as strong as they were when they get rehoused and will not lose power, like Sauron did when he had to fashion a body for himself. Hmmm, come to think of it, it is debatable actually whether the act of creating a body costs any power, though the shape of the hroa and the time it takes to create are definitely correlated with the power someone possesses (Melkor and Sauron losing the ability to take fair form and the time Sauron took to create a new body after the fall of Barad-dur are good examples).
As for your other questions that haven't been answered yet:
#1 Why do I think Beren to be a dummy? If he wanted all three of the Silmarils, he should've just taken the iron crown of Morgoth & back to Menegroth.
Well, Morgoth was a big lad and I reckon that Iron Crown would've been quite a burden. Besides, Fate decreed that Luthien and Beren could only take one Silmaril (which is why the blade broke after Beren attempted to get another one)
#4 The passage below gives me the impression that the children of Finarfin were skilled in magic & enchantment.
Quote:
By the arts of Felegund their own forms & faces were changed into the likeness of Orcs;
The Silmarillion - Of Beren & Luthien
Maybe Finrod was a very good make-up artist?
#5 If Huan had lived during the time of Sauron, would he be able to win against him with his ring on?
Good question that one, really. My own bet would be no, unless Sauron decides to try his hand at another fight with Huan like the first one.