These questions are answered in any "How Bitcoin works" type of article.
I would try to respond item by item here, but the way they are asked betrays some ignorance about how the system works in general. So I would suggest reading about Bitcoin first, and then asking the parts which you don't understand or don't agree.
The "odds" could be considered an interesting question, but I don't understand what the asker meant. The PoW done on Bitcoin is immense, and none of the alternative currencies can really approach the low probabilities Bitcoin has. This won't produce interesting numbers for you. If the asker is in fact interested about potential differences in hypothetical cases, then s/he needs to clarify.