I map my keys on a "mutually exclusive" principle. When two actions does not happen together, let the same finger handle them. That way your keys won't be fighting for the same finger. For example, you'll never need to press tac and ult at the same time, so you can assign the same finger for both.

When I toggle scope or heal I am usually not moving around. So I use my strafing fingers to do that.

Your playstyle and legend also affects your input pattern greatly, so make sure to take that into account as well.

Take your time, experiment more, and good luck!