Its a good idea to wait until spring. Pick up some of the mulch from your town, turn it and add some grass clippings and vegetable scraps to it this fall and by spring you could have some real good compost. Alternatively, mix the mulch in with your clay in your dirt pile and let it work over the winter. In the spring use your new FEL, which you can justify through the savings in never, ever, having to buy topsoil or compost, to haul it over to your driveway.

The biggest difference between compost and mulch is time and temperature. Compost is decomposed mulch and other organic matter. To get rid of the weed seeds you need to ensure that the pile is aerated (turn it over once in a while) and has a reasonable mix of carbon and nitrogen. With a good carbon/nitrogen mix and aeration you will get a lot of aerobic decay and the pile will heat up to well over 130 F which is hot enough to kill the weed seeds.

HazMat's time/money comment was apt. If you enjoy the doing spend time, if you want the result spend money.