MM. Wiccan High Priestess here, with a few points. I'm going to address your second question first. There are absolutely people who identify as Christian Wiccans or Christian Witches, however there are many Wiccans and Christians alike who argue that the two ideologies are not at all compatible. There are many reasons for this, and one of those is that Wiccans do not generally believe in a fall from grace that requires redemption by a messiah, while it appears that the need for spiritual redemption is a core belief of most Christians. There are many other incompatibilities as well. That said, there is a man in my Wiccan Tradition who goes regularly to a (very liberal) Baptist church. So basically, it's up to you, but just know that if you identify as having both Christian and Neo-Pagan Wicca-based beliefs, you'll encounter a lot of people who will challenge you on it.
Notice that I said "Neo-Pagan Wicca-based beliefs." In Wicca, there are different Traditions (like Christian denominations), and the teachings are passed from Initiate to student through study, supervised practice, and formal initiation/elevation. There are many people who believe that Wicca is "whatever you want it to be." This isn't true. Those who read books and create their own practices are eclectic Neo-Pagans. There's nothing wrong at all with practicing eclectic Neo-Paganism. But it's not Wicca.
Regarding an appropriate athame (which is some times used in various Neo-Pagan practices, not just Wicca), it depends on whom you ask. To me, an athame is a black handled, steel bladed, double edged dagger, approximately wrist-to-middle-finger-tip length that has been empowered using a coven sword and presented to an initiated Wiccan. Otherwise, it's a knife. However, many eclectic Pagans dedicate their own blades, and some times they even use ceremonial knives that are made of obsidian, wood, or quartz crystal. So really, if you are an eclectic, you can use what works for you.
Credentialed Wiccan High Priestess