"How long until he makes a decision?" Can take a while, don't remember it taking more than about 20 HBD days but I could be wrong.
"And what are the chances he signs?" Used to be nearly 100%, now several of these are refusing to sign, but it's still very high. Don't increase your offer-- wait until he responds, then meet his new demands and he will sign 100% of the time. If he responds by saying he won't sign, use the link from the "email" he sends you to get back to his negotiations page and make the same offer again, he may well sign this time. Don't delete his reponse email; it may be your only route back to his negotiations page.