I have the 0.3, 0.6, 0.9 ND grads in both soft edge and hard edge. I don't think I ever used the soft edge, the edge is just too diffuse. With wide angles, be sure that you get the recessed wide-angle adapter as otherwise you can get vignetting. On my Zeiss 21 mm with 82 mm front thread, I can use a single slot plus the polarizer without vignetting on the FF 5dmkii.
The 0.9 ND grad cuts three f-stops, which is a lot. I frequently use the 0.3 and 0.6, and if need be, they can be combined (remember multiplication [not addition] of extinction factors). In digital that is not too much of a problem, but shooting LF film, you better get your filter factors right. If I remember correctly, the set is cheaper than the individuals.
You can also use the pol filter as a solid ND 0.6 filter. You don't have to cut reflections out, so depending how you turn it, you can get specular highlights, if desired. The ND grad have sufficient large ND area to use them as a solid ND filter (without gradation). If you do not use -10 stops too often, you can combine ND and Pol to get close to -10 stops. You get additional surfaces, but if budget is a concern, give the combo approach a try.
Last but not least, consider getting a compendium hood. Added filter surfaces invite reflections to creep in. Hood and Pol cannot be use together. In that case, I use a piece of cardboard to shade the lens. I haven't looked for a 105 mm hood.