Answer: Absolutely you can do all the planning and preparation, all the hardscape, all the soil preparation right through mulching. This is in some ways better. You will have ample time to plan and do the installation. You can do thorough soil preparation -- remove existing vegetation/control weeds as needed, loosen the soil, test it, add the organic matter and any other needed amendments as indicated by the soil tests, smooth and level the soil, and it will have time to settle so you can double check the grading and leveling prior to planting.
In many ways it is better to take your time with the prep work and then plant when everything is ready, rather than rush and try to do everything at once. When everything is ready, including a detailed planting plan, the actual planting is a snap. It sounds like you are planning some extensive projects -- you may need several months to get ready to plant anyway!
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