How to add Autocomplete to a Views Custom Textfield Filter
So it turns out that I just had a small typo :( Anyway, I'm keeping this question up in case others are having troubles since it outlines completely how to do this and I was personally unable to find any tutorials. 

In the above code it needs to be #autocomplete_path instead of #autocomplete.

Furthermore, if you are trying to create your own custom autocomplete filter, remember that you have to indicate the file containing your handler class in your .info file (ie: files[] = views/handlers/name_of_my_handler.inc) and that you need to assign your handler to a field using hook_views_data() or hook_views_data_alter().