ok make sure your credentials are correct. example, when entering make sure 0 is not o and might be case sensitive. so confirm your credentials with your guy. if possible ask them to change credentials then try.
depends on your vpn provider. do they update regularly and if yes do you update their app? also, set specific and closest and fastest server might help. do you setup automatically connect vpn at startup or manually? its completely on your hands now to play with these settings until you find out whats the best setting for you because vpn servers my work good for few hours then may not later and you have to switch to best. so best thing is manually select best every time you wanna watch.
I won't temper internal but I dont know if or which external wifi adaptor will work however, I would say buy an extender with an ethernet port and leave extender next to your box and hardwire from extender to the box.
try to turn on cec on your box and turn virtual switch off then try. I had one time similar issue with 4900 and Samsung 5 series and I turned off virtual switch fixed me issues. you can try that as well let us know
should post in 4900 section. what display seating are you talking about, display and sound, hdmi-cec, and power, screen position? need some more information. what app version do you have? post some info.
just on safe hands for future connect your device on serge protector and buy your self few dollars outlet tester to test if your outlets are fine in the house. this will prevent from future damage.