1. graduated here is related to the word 'gradient' meaning that you go from an area of high density to an area of lower density of something. In this case, the wires will be spaced more closely together at the bottom and with increasing distances between them towards the top.
2. Yes, even a sentence that ends with numbers needs to have a period at the end. It might look a little unnatural sometimes but it is necessary. If there is no sentence afterwards though, sometimes people leave it off in informal pieces of writing
3. You can't use real in this sentence and while the sentence could be rephrased, physical stock is definitely going to be the most common phrase. Physical means tangible - it can be touched or held. Real just means that it exists but it's not necessarily tangible. For example, music is real but not physical and thus not tangible.