So to get it clear - you want to show nothing if 4 or less characters have been entered?
I don't think you can use the standard Item Type here - if you want that functionality you would have to use a plugin.
are Plugins that can be altered to give that capability.
You need to know jquery to do that. There is a variable minLength (in the file apex.vcplugin2-widget.min.js) - set it to whatever value you want (in your case 5) - if the number of characters is less than that it will not search.
Hope that helps.
You can use the Select2 APEX plugin in case you are on version 4.2 of APEX. The plugin has autocomplete functionality built-in and allows you to set a minimum length on the search term. You can try it out on the demo page. Please note that there is currently no support for lazy loading. That's something I'm working on... More information on the plugin here.
If you want to stick with the apex item, I'm afraid you will have to create very bad JS hacks to reach your goal. The Number of Chars is not in any way easy to reach - the following Thread might be interesting in this setting:
Personally I would go with Nicks Plugin - except for the lazy loading it can do all the stuff you need.