Out of curiosity, which one did you get?
But yeah, a case is definitely the first must-buy (went case-free for years, changed my mind recently as I dropped my P7a on concrete for the third time 🙃). No MagSafe ring for mine, but I got a Ringke Onyx case. It's pretty cheap, looks great and even makes your phone much more pleasant to hold.
Maybe try changing the Wi-Fi band ("Wi-Fi Hotspot" -> "Speed and compatibility" menu)? Check also if you get the same slow internet with USB tethering.