How to start Tunnelblick VPN connection via Terminal
A possibly better idea than messing around with openvpn directly (Tunnelblick is basically just a fancy GUI around it) would be to use an Applescript, something that can definitely be launched from the terminal (i.e. with osascript)

Example taken from here:

tell application "Tunnelblick"
    connect "Company_VPN"
    get state of first configuration where name = "Company_VPN"
    repeat until result = "CONNECTED"
        delay 1
        get state of first configuration where name = "Company_VPN"
    end repeat
end tell


You'd write this into the Script Editor, save it, and then you could launch it from the terminal with osascript, or by double clicking on the script.