It looks like I've come across the double-edged sword of promoting your wiki as it also invites potential trolls and vandals. Although I was prepared for it happening since it IS the Internet, it is still disappointing for me as an admin to come across such events. I took it as a learning experience and it is something every wiki needs to go through so perhaps that was this wiki's Internet rite of passage.
Of course, this illustrates the need for some sort of policy when it comes to dealing with anything that might require banning. I stuck with the good ole "Three Strikes & You're Out!" rule of warning and banned the user (including the IP since they returned as an anonymous user) for the time of 2 weeks, as well as protecting the page in question (a blog post in this case) against further edits. I was tempted to do a perma-ban but based on the illiteracy of the user in question, I think they genuinely didn't understand why what they did would be considered vandalism or spam so hoping those two weeks will either give them enough time to come to an epiphany about the nature of vandalism/spam or get distracted by other matters more fitting to their nature such as another wiki more suited to their needs.
However, I really don't want to set out too many policies right off the bat since it reeks too much of being an overly authoritarian admin in my mind and I would still like to foster a welcoming mindset-- especially if this will encourage users to become regular enough editors that I can consider promoting them to be admins on the wiki. So we'll see for now. This wiki is still small enough for things to be decided on a case by case basis so I will still play it by ear.