Always remember seeing this game here on GOG since I first found out about the website. Thinking of getting it now, but I don't own a HOTAS or Joystick. Is the game playable without one or is it one of those more hardcore sims where it's practically or literally mandatory?

Though you can easily do without hotas a 4 axis joystick (x-y, rudder, throttle) is recommended.
Still, you might get away with keyboard (I don't remember it supporting mouse steering) since the Apache heavily relies on guided/turreted weapons and don't need precise aiming, except for the rockets (somewhat).

If you eyeing to get Hind I don't think it will be fun with keyboard only as too much weapons require pinpoint accuracy.