8 Reales Questions.?

The weight of counterfeits can vary greatly, it can also be exactly correct. But when it is correct, usually the size in diameter or thickness will vary slightly - or they can just use another metal that equals the weight. The point is, there are many variables possible, that includes them being too heavy, and correct weight does not constitute authenticity.

Yes, it could. But circulation wear is usually not that much. Depending on the coin of course, it varies with denomination and metal, circulation wear is often only a few hundreths of a gram. I can't think of a single case where I have seen it be as much as 2 tenths.

Again yes, but rarely I have seen corrosion be in perfect little circles. Usually corrosion pits are oddly shaped.

Absolutely.

No, most modern fakes, that I have seen anyway, are cast. Minting with dies is a very expensive process and usually requires a level skill that is beyond most modern forgers. It can be done though. In the middle part of the 20th century there were huge business in making counterfeit gold coins. I'm talking full blown factories, warehouses, distribution networks - they rivaled and even surpassed the legitmate mints of several countries.