If you have an etching question, email me, and I will attempt to answer it here, if I can't, or have no experience in it, I will post it under questions below. My answers are based upon personal experiences. There are many variables to consider when sand etching, I do not guarantee results, and assume that you take appropriate safety precautions when working with glass and sand blasting or acid.
I prefer to use your name, and city, for your questions, but will not include your email address.
I appreciate hearing back from you whether my comments and suggestions are helpful or not; as I'm not getting any monetary return out of this, this is the only reward - right? :-)

Interesting... Where to start? Firstly, can you not use glass mirror? This is sort of a mixed up answer, but I think it may answer some questions for you:

I have found that there is a slight trade off between having glass (which is relatively scratchless) and plexiglass (in order to avoid either the breakage concern with glass, or the weight of glass).

One advantage of pleximirror, is the range of sheet colours (there are 20, though not all of these are always available). Plexiglas is a trade name for an acrylic product. If you must use plexi/acrylic for weight or breakage concerns I would suggest that you should get Abrasion-Resistant Acrylic Mirror. This product while not completely scratch-proof, increases it by about 30% (it is though somewhat more expensive to purchase). Plexiglass comes in 4' x 8' sheets (and can be special ordered larger) with up to 7 thicknesses to .25 inch.

One reason for scratching plexi, is that mild detergents and a soft cloth are supposed to be used for cleaning, not Windex or ammonia products which in themselves will scratch the product. If you are using a hand cut or a computer cut resist, try to remove only enough of the plexiglass protective covering to allow the image portion of the resist to be on the plexiglass itself.

I get my acrylic products directly from Laird Plastics, a large supply house in Canada and US. You should be able to also purchase from them, as you will be reselling the product. They will sometimes just sell you the size piece that you require, rather than the full sheet (4' x 8').

Are you breathing in the fumes from the cream as it's etching? It should only be used it in a well ventilated area, and do not breath the fumes. I would expect that even though I have never gotten a sore throat from it, it is possible - it is a chemical reaction between the glass and the cream. I would suggest not using again before doing the following:

You may have a reaction to the chemicals in the etching cream. Try contacting Armour Etch about side effects. If my memory serves me correctly, Eastern Art Glass is a division of Armour Etch. You might try them for some help.

I would also suggest (strongly) that you should get a respirator that has replaceable filters rated for acid fumes. A respirator like this costs about $80 (Canadian) it can be purchased in safety supply shops. It is a cheap insurance against health problems. You have to get the correct fit in the mast, and as long as it fits snugly to your face, you should not be able to breath any of the fumes. (That is as long as one doesn't have a beard as I do!! I get around this by wetting my beard before placing the respirator on.)

Does it require a lot of talent? Well, if you can draw it helps, but this is not a prerequisite.

I have some suggestions for starting glass etching in previous versions of my Q&A (#1 has some important precautions that SHOULD be followed, #2 has some suggestions on starting). Also, I found an article titled: Sandblasting, by Roger Smith that should answer many of your questions about how to start.

I would suggest anyone starting should try to cut some resists (stencils) on some glass (even window glass will do for this), and take the pieces to a sand blasting shop, (or an auto body shop might etch them for you) and have either the shop etch the pieces, or if they'll let you use the equipment, blast it yourself (in a cabinet only, unless you wear protective clothing and a respirator). This way you can try out the craft, with a very minimal expense see if you like the results, and if it is something that you wish to go farther in.

The glass inks that I use, I came across a number of years ago, when I contacted an ink company in Canada who in turn sent me some information on their inks (including ones that can be used on glass). When I got the info, there were so many safety warnings, and precautions that it almost scared me to use the product (for instance: "repeated breathing of vapour may effect the central nervous system" "use of protective clothing is recommended" "skin contact - immediately wash well with soap and water"). These are not just another oil based paint, they are, by the manufacturers' suggestions VERY dangerous. I am sorry, but, I will not pass on the company name, or the product name because of this. I don't know of other inks or paints that are safer, but I wouldn't mind finding them.

If you are interested in finding more information on glass inks, contact an ink supplier in Nevada (for screen print items, or glass or plastic containers), tell them your application, and they can suggest a product that will best suit it.

I have no experience with an airbrush, but with the precautions that came with these inks, I would NOT try to spray them onto glass.

The resists used for Hydrofluoric acid years ago would be wax, you would coat the glass with wax, and then scrape off the image that you wanted etched, and immerse the glass into a vat of acid - this acid is extremely dangerous, and I don't know if it is even obtainable now owing to that fact. If, you mean the acid paste that is currently sold for etching glass (a mixture of ammonium and sodium biflouride) you can either get pre-cut stencils from a variety of sources (see Q&A #1) or, you can cut your own from self-adhesive vinyl (also called contact paper, shelf liner, etc.). If you cut your own resists, you may have to try a number of different brands of vinyl, as some don't stick as well as others to the glass.

For sand etching, you can also use the self-adhesive vinyl (as above) or a variety of other products, in Q&A #5 I have a link to an article by Bob Pickard in the Useful Web Links section with a number of suggestions on the resists that can be used.

As far as where to get the materials, most department stores will carry the vinyl, photo resists can be purchased from either Rayzist or Photobrasives (both these are linked back in Q&A #2).