"Another thought is to use a separate box for the 10's but hard for me to say without more details."

That's an idea I've been entertaining as well.

" I assume that you will crossover to the 4" mids in the 100-300 Hz range..."

Exactly. I have high sensitivity (~97db) subs/bass boxes already, but they really start losing their charm above 100Hz. Everytime I want to think about a new array using say, 3 inch drivers, or any other type of speaker with a mid range that needs crossing at 250-300hz, I'm stuck with no way to bridge the gap between them and the subs. If I build the bass array separately, I could use it for other projects.

"You did not say whether you plan sealed/vented/open enclsoures so it is hard to guessimate how the bass will react. My personal preference is for sealed enclosures for their better transient response."

Ditto here too. I want to use sealed all the way thru.

Thanks again.
Allan