A metal wire sticking out of tire means you have a flat waiting to happen. Check your tire pressure, get it to a shop, have the wire taken out and see what they have to say. If it’s in far enough that it’s punctured the tire, you’re going to need a new one.
As far as tire wear goes, the easiest way to tell is to look for wear bars inside the tire tread itself (i.e. the grooves cut into the tire). A wear bar is a slightly-raised bump of rubber inside the tread that indicates the maximum amount of wear your tire allows. When the tire is worn down flush to the wear bar, it needs to be replaced. Usually it’s better to replace slightly before then to be safe, but if you’re nowhere near it, you’re fine. If your tires don’t have wear bars, get a fine ruler and try to measure 1/32″. If you have more than that much tread left, you’re good.
Also be sure that you aren’t using a worn tire in the back and a new tire in the front or vice versa. That can adversely affect your handling.