The answer to your second question is that numbers can represent many things. They can represent bad words and good words, etc. There are two things to keep in mind here. One is that number 786 is not a proper substitute for Bismillah. . So, if somebody writes 786 instead of Bismillah it is not like writing Bismillah. Also, if somebody utters this number instead of the actual Bismillah then he would not have the reward of saying it. . Also, if somebody wants to use the number out of respect just to seek blessings then there is nothing wrong with that either. This could be done, just in utterance or in writing. Usually, things are also based on the intentions.
