Power distribution in three-way speaker systems

Kilowatt, sorry I didn't get back to your question regarding the number of horns sooner. It looks like you have a fair grasp of the issues here. The power splits that I quoted are guidelines only, if you like chamber music it will be totally different than rap, just wanted to put in the caveat.
60/40 split (around 500Hz) would suggest that you would need 1.5 times the acoustic power for the bass than the mids/highs. Maybe 6 horns and 600W, though I always like to have my mids and tops idling even when the bass is flat out so I would go for the 8x800W.
Kilowatt, get the Yamaha Sound Reinforcement Handbook by Gary Davis and Ralph Jones. It costs less than $25 and will save you money!

Regarding a 3way split say 250Hz is the 40/60 point and 500 is the 60/40 point then between 250-500 would be 20% below would be 40% and above, you guessed it 40%. All explained in the book.
While I'm on the subject, can anyone suggest other references?

Regards WALKER