According to the data sheet and the manufacturer's website, the maximum memory card expansion is 128GB. That's also what the specs say. The only accessory I have seen is that Digitec also lists the 258GB. But it doesn't say that this is supported, as I think.
On receipt of the goods? Yes. However, this is not necessarily intended as protection for everyday use. These are usually removed. Some even leave it on until it comes off at some point. As I said, this packaging film usually does not offer much protection. Enclosed is a suitable product: Hama screen protector for Honor 5X (2 pieces)