Answer: Tilling the soil will actually bring more weed seeds to the surface where they will germinate, so it would be better not to disturb the soil any more than necessary. You might want to control any existing weeds using an herbicide containing glyphosate. Read and follow the label directions.
Once you spread out the fabric and top that with gravel or stones, hopefully no vigorous perennial weeds will regrow from their roots and pop through the fabric. If they do, you will need to spot treat with the herbicide.
Over time, any organic material trapped between the stones will break down and create a seedbed for seeds to germinate in. (The wind will bring in seeds.) A periodic raking and/or herbicide treatments may be necessary to prevent these seedlings from growing in your stone bed. You might want to use a pre-emergent herbicide such as corn gluten to prevent crabgrass from germinating as well.
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