Current, Amperage

Just buy more power than you will ever need.
Too much is good, not enough is terrible.

Other considerations which may mean a lot after you find out..
Class A. Remember the power bill will go way up, plus plenty of heat.
Plenty of heat added from having a tube amp also.
Generally the IDLE wattage of the amp in the measurements will tell you the efficiency.

Do you want to leave the amp on 24/7? Then a Solid State amp is required.
Remember tubes need attention.

What are the impedance of the speakers? 8 ohm or 4 ohm?
If 4, you need to check the 4 ohm rating. Some double, other no where near double power to 4 ohms from 8

If 4, you need to check the 4 ohm rating. Some double, other no where near double power to 4 ohms from 8

Just because an amplifier can't double its power when impedance is halved does not indicate that it can't behave as a voltage source.

@elizabeth 

Thank you. 
I agree, and this IS the point of the discussion; What is enough [we know too little is bad, but how much overkill does one need ]?

I had a McInotsh MC252 - 250 WPC on either 2, 4 or 8 ohms, and I loved it, but do I need that again in a 12x12 room? used for $3500 for my type of setup is a lot. I don;t need the 'Wow' blue lights factor again :)

Can a Rotel 200 wpc or something else provide enough [that will be good] without having to spend more than $500-1000 used? 

Thanks; this is an interesting topic for all of us that have decent systems but maybe not more than $5-$10K into them. 

You don't need anything like that power in that room. You need maybe 50 watts if you want volume loud enough to destroy your hearing. 
I do NOT agree with recommendations to just buy more power than you'll ever need. More gain means more gain stages which means more distortion, and big iron seldom competes well with a quality lower power amp with simple topology. That's the entire basis upon which tube amps are built. 

It's more about synergy, not math.  I have a 300 wpc Mac but usually am using my 10 watt triode.  Running out of power can ruin a speaker and/or your experience but quality is much more important than quantity.  

My math was a generalization but you do need a frame of reference on these things.  Generally speaking you gain 3db for doubling your wattage is a great way to understand why going from 40 to 60 watts is virtually inaudible all other things remaining equal.