In response to the SSD drive - it is presently 256 GB PCIe® NVMe™ M.2 SSD, so I would think a lager capacity drive that fits in the same location would be just fine. Keep in mind this is a M.2 card drive, so a larger capacity drive is doable.
Now for the WiFi - the installed WiFi chip is not 5GHz. It only supports 2.4GHz WiFi. Is identified as Realtek RTL8723DE 802.11b/g/n (1x1) and Bluetooth® 4.2 combo. In this thread, for a different model laptop, it states a solution
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