As you plant you will make changes. Each year it will look different whether you want it to or not. Some things will do well and others will languish. If you expect your garden to be a constant like your living room with each item carefully placed and selected for color and size, then your garden will constantly frustrate you. Just imagine the couch getting bigger every year as it overtakes the end table.
Maintenance can make or break a garden.
Be realistic about the time you have for maintenance. You may have a beautiful design with great plant selection, but it will quickly fall apart if it isn't maintained. Actually another word for maintenance is therapy, but no one wants to be in the doctor's office all day. Mulch, mulch, mulch. It reduces weeding, watering, soil temperatures in summer and adds organic matter as it decomposes.