Shall I answer all of these questions one by one and test you over them? I think not; I don't believe tests accomplish anything, anyway, unless they're telling me which Star Trek character I am the most like (it's Bones, in case you're wondering).
To put it succinctly: consistency is key. While adding "th" and "rd" to numbers is a variety of written slang, it is acceptable in many settings. Not all - if you send me your research paper or business presentation with any of these rather than the actual numeric word, I'm shooting it down. But your blog, website, or poster? Totally fine. Your novel? Honestly, as long as you do the same thing throughout the novel, it's acceptable. Consistency matters much more than your choice of term.
So, don't wish me Happy 4th of July for the fourth time. Don't tell me that your second cousin's birthday is the 2nd of the month. For the first time since I began writing this blog: Happy Fourth of July!