THank you Whitefire and CarlR

It's difficult to make generic suggestions but on the whole, I think go with easier to use grads first ie
try what results you get with a 2 stop ND rather than a 9 or 10 stop
try what results you get with a soft edged GND rather than hard or reverse edge - maybe start with 2 or 3 stops as well?
don't go all out with the most expensive stuff unless you think that after using them, GNDs are the way to go for you rather than exposure blending
and of course, a circular screw on polariser