I find many tutorials on how to open sublime text 3 from the terminal via creating a symlink etc. But I'm not really sure on how to open a terminal in the location of the currently opened file from within sublime. I'm using an old macbook with High Sierra if this makes any differnce;)
You can use this plugin, Terminal, it opens a terminal tab on the directory of the currently selected file or project (if you have one open), you can install it through packagecontrol, you can configure the key to launch the terminal, and whether you want to use iTerm or the default terminal app.