Snow and rocks

Yeah it varies a little but certainly more than a foot with quite a bit deeper in places. It has been very dry up here or we wouldn't have even entertained doing the work at this time of year. The plan is to wait for the first warm dry spell (often late April/Early May) and then hopefully have a go at sorting it out. Has anyone used a Blec Stone Rake on a heavier soil?

I'm in the process of levelling and clearing around half an acre at the rear of our house with a slew digger and am now thinking about how best to prepare the ground for seeding. The top soil (50cm+) was stripped to allow the subsoil to be levelled out and then replaced with the digger. It is quite heavy clay but seems in reasonable condition. I'm up in Aberdeenshire but have managed to find local hire company with both a Blec stone rake and various sizes of rotavator available to hire. Will the stone rake work on heavy soil and would i need to rotavate first? Any tips or suggestions welcome.