Posted: 18/06/2014 at 23:24
I think you'd be in danger of bits of metal flying off the rotivator, they're generally meant to turn over soil (unless anyone knows of a super industrial type). I'd personally stick to the pick axe and focus on the exercise element of using it
The cow manure would be best left to rot down, or if you have a compost bin put it in there and let the worms mix it up with the rest.
If you've only got subsoil you'll need some top soil before you can seed it. The rotted manure would help as a soil improver and add some nutrients, but it won't much transform the subsoil into a good medium for seed. Even if you bought turf, it still needs laying on a decent bed of top soil