Materials used. I'm guessing most if not all horns are made of brass to some degree (percentages) and then covered either w/ lacquered or plating. Or UL. Or are most starting with simply a steel body?

Most agree plating does nothing to affect the sound and is just cossmetic. 

But is there a noticeable difference with a "solid brass" or "solid copper" sax (e.g. Rampone & Cazzani...Antigua Winds' Power Bell line has offers it in 10 different "finishes"...one they call "classic brass body and keys" and another "Vintage Copper body and keys". They do mention when a finish is lacquered or a plating. Does that mean these are also plated finishes but just chose not to say so? Or are they mostly "solid" brass or copper? 

There doesn't seem to be many makers of horns that say they make "solid brass" or copper horns. The only other one that is making that claim is "Sax Gourmet" (besides Rampone & Cazzani). Are there others we know do make actual brass or copper horns??

Since brass is an alloy made of copper and zinc. And Bronze is also an alloy made of 12% tin and the rest copper. When a company says they can make a "solid copper" sax...are they? Like Rampone & Cazzani. Could it be made of pure copper and not made into an alloy too for strength...adding a smaller percentage of either zinc or tin...or some other metal? 

Was talking to one of the people at one of the authorized US R&C dealers. Said the "solid copper" horns are, as I guessed, just closer to being 100% copper. But still an alloy..I guess for the needed strength. As 100% copper might be too soft. 

It's terrific, I think, R&C can still make their horns 100% from start to finish making  their own parts. And doing their own assempy. Last so long in the business. And offer their horns at a reasonable price.  How they haven't given into economics. Like Selmer has (using the odd Taiwanese parts). 

Are there any other makers who make 100% of their horns? Or is it only R&C? All other horns are part Taiwanese (perhaps only the Japanese brands?? Or are they using some Taiwanese parts too?).

This is a fairly tough post to reply to because you mention that you want a bright tone, but also very warm.  One thing I recommend is checking out the alto sax mouthpiece reviews from Steve Neff.  One piece that might interest you can be found here:

http://www.neffmusic.com/blog/2017/01/phil-tone-jz-alto-saxophone-mouthpiece-review/

Also, if you are looking for better tone, you could consider trying a softer reed, maybe someting like a Rigotti Gold 3 light.  I would work with mouthpieces and reeds first, and hold off on ligatures until after you find a mouthpiece/reed combination that you like.  In general the impact of a ligature is small in comparison.

Good luck!