Not an expert (or a chemist) on the subject by any means and I could be completely wrong but:
1.) Lime, NaHCO3 (Baking Soda) and Chalk are the general choices. Lime is usually #1 on the list, followed by baking soda, then chalk. Lime seems to produce the best and most neutral result.
2.) A formula would depend on the acid and the alkali in use. It doesn't require much of either because their isn't a lot of buffering (alkalinity or acidity) in the invert syrup (easy to move the pH up or down). The amount of acid required might be more due to the alkalinity of the source water. It would need to neutralize the waters alkalinity in order to lower the pH of the sugar solution. Also those alkali listed in #1 are chemically very powerful and change the pH fast. A brewing water mash/sparge calculator would most likely suffice for a guesstimate or perhaps a 1/4 - 1/2 tsp of acid and an 1/8 - 1/4 tsp of alkali per 1lb of sugar being inverted.
3.) It's not necessary but some of the benefits would be to a.) stop the inversion process (maintains the color at time of addition), b.) match the wort pH in the kettle (or getting close), c.) render the product safe(r) and more pleasant for consumption raw, d.) microbial resistance, e.) aid in maintaining the syrup state. The Baking Soda and Chalk will most likely leave salts of calcium and sodium behind after the reaction along with the acid anions malate, citrate, lactate, phosphate, chloride, sulfate, etc.... depending on the type of acid used. Most likely not in significant amounts but still something to consider.