Which Tweeter preferred- dome natural material, Beryllium/Metal or Planar Ribbon? Why?

Depends, but Magnepan seems to have the best.  The Decca ribbons failed a lot, unfortunately, but maybe they have improved them.

I BELIEVE (don't shoot me if I am wrong, it has been a long time) that the idea is to move as little mass as possible.

Evidently, along with the best (most accurate) speakers on the market, Magnepan has come up with a ribbon-style that is hearty and accurate.  Not bad!

Cheers!

@asvjerry 

Apollo Speakers

https://www.audiogon.com/listings/lisa0ffi-the-apollo-system-high-sensitivity-ob-line-source-amt-based-system-the-apollo-full-range

I would love to hear them.  

@danager Well, Charlotte is but 2ish hours from me.  I suspect the dealer would take one look at me and accurately judge me a 'lookie Lou'.  So I'd have to talk extremely fast, rent a car that would require return Immediately if not sooner, dress beyond spouse's comprehension, and enter with some willowy blond that would also need to be....'rented'. *L*

But, agreed...I'd love to hear them as well.  It would spoil me worst than being staked out in the yard for a month after untimely demise (although some here would demand a stop-motion vid to verify that fate...). 

Meanwhile, the 30K$ is a bit of a pause...but being the sneaky SOB I can certainly aspire to....

ESS will sell you direct 18 of the large Heils' for $3,582 plus tax & shipping.
They're heavy, so the latter will be substantial.
Throw in the extra $18 and you can have 18 BT adapters and a choice of 2 versions of headphones....wipe out your gifting for years... ;)

They offer their 10" woofers for 149$ each....get as many as you think you could tolerate....the passive radiators for them are 110$ each, but to duplicate the Apollos'. not really required....

Crossovers...I'd go with some pro version.  I like my Behringer 2496 and you can tweak yourself into a puddle...*teehee*

OK, you're down about 5~6K$.

Cabs...Heils' are dipoles, and ESS doesn't 'cab' them....why should you?
I can suggest a line source frame that would make wood blush, but I'd go with aluminum.

Woofer cabs....Apollo's are lovely, but the design is ancient.  Personally I work in wood, so not an issue....for me, anyway.

Sweat equity in assembling something that'll crack sheetrock. *Evil G*

I've just saved you nearly 20K$.

I'll bill you later.  ;)

When would you like to begin?

Regards, J.

(ESS ought to give a discount on a 'bulk buy', but they've already discounted on them....Promise pics of the end product....;)...  The Heil AMT is too good to let fade into obscurity or bankruptcy...and NO, I'm not a dealer and I don't get a commission on anything.  I'm just a fan....)

Y’all could do so much better if you’d try....Really.

*kicks soapbox into the corner...

Do this simple exercise.  Disconnect the mid and bass drivers leaving only the tweeter.  Play some music.  It's impossible to tell if the tweeter is good or not.  Meaning one can only tell how good a tweeter is once it is integrated to the rest of the speakers.