The string you pass to httpProxy needs to start with http://
createConnection is not a valid option for the SteamUser constructor. To use a SOCKS proxy, you should use the socksProxy option.
Can't be done. You can get a web logon nonce from https://steamcommunity.com/chat/clientjstoken but that's not the same thing as a refresh token for the client; you have to send that as web_logon_nonce in the CMsgClientLogOn message.
You would need to download and parse items_game.txt, look up the sticker by its sticker_id, then fetch your appropriate language file to translate the localization key into an actual name.
Those xml endpoints are pretty unreliable and anything that uses them should probably be considered deprecated. Using the WebAPI for anything that it covers is going to be your best bet.