2. Cross them aboe 3500 Hz for no loss in omaging that you will be able to hear.

3. No they will not consume much power. How much power do you think it takes to drive a small dome like that? ALmost none!

4. THe crossovers you use may consume some power. If you go with a simle 6db/octave low & high filter, and get the crossover points right, my guess is you will have a much better sounding system.
-akhilesh