I moved into my new house July and we were looking forward to playing in the new garden. Unfortunately the previous owners had for whatever reasons buried bags containing grass cuttings in the garden, making the whole garden on about 6 different levels.

What I want to do now as it's too cold to be playing out side is to take up all the grass (which is in clumps anyway and needs removing), remove the bags and level the soil out. Then put down some grass seed and make some planting areas. Is it advisable to do this as I am a little concerned about turning it into a quagmire...

The garden is about 35 x 35 foot square...