I would do the whole area you intend to plant at once. No sense in doing small sections piecemeal, unless you aren't certain just how large an area you want to plant. If you know what you want the boundaries of the bed to be, I would just lay it out and start digging the whole thing at once.

I agree to do the prep for the whole area at once, removing/killing the grass and making whatever additions of compost, etc are needed. Then mulch the whole thing to prevent weeds from getting started and plant as you have time and energy and as plants or seeds are available. Here's a thread on the perennial forum about starting a bed that includes photos of beds in process, and suggestions of what different folks do to get the area ready to plant.

Thanks so much! I'm doing more reading on lasagna beds. Knowledge is power! Can't wait to start on this project. Just need to find my 'layer' materials. Fall will bring me many leaves and I've started a small compost bin, so I am part way there.

That's a large area to do lasagna beds on without getting materials from elsewhere. Check in your area for free or inexpensive sources of material for your lasagna beds. For instance, I get manure from the horse farm down the road, but pet rabbits, chickens, llamas all could be sources, and my local dairy farm will deliver a truckload of manure for a fee. Wood chips to use as the top mulch layer can often be found if you pass tree trimming crews in your neighborhood; I've found them more than willing to dump in my driveway rather than having to haul them to the local transfer station across town. I also get wood shavings from local woodworkers, and have gotten sawdust from a pile at a local sawmill that had gotten wet, so unsuitable for horse bedding, etc. Some towns have compost made from the fall leaf collection, and when we were first starting our garden, we picked up bagged leaves by the side of the road to increase our compost quantity.

If you decide to purchase it, get an entire truckload of compost or bark mulch. Most yard supply companies will either let you bring a pick-up to haul it yourself or will deliver an 18-wheeler. It's much less expensive by the truckload than by the bag per volume.

I use multiple layers of newspaper or a single layer of corrugated cardboard under the top mulch layer to discourage weeds, so you can start collecting those from the grocery store or appliance deliveries, etc. If you don't mind looking at a somewhat homely view for the summer, you can put down plastic with the edges sealed with boards to solarize the soil and kill seeds and the grass that are currently there. That will help by decreasing the volunteer weeds and grass when you are ready to start creating your beds and planting.

You've received great advice/tips from the posts above. N.B.*: brown, recycled cardboard is often available--free--at grocery/liquor stores. Healthy soil has fat worms that poop. Worm poop is a natural organic fertilizer. Worms LOVE cardboard so write that down. If you have healthy soil, your plants, whether purchased from a local nursery, or mail-ordered online, so long as they're carefully planted and hydrated immediately after planting, will thrive.

N.B.* (Latin for note well)

Fertilizing generally won't make your perennials grow faster so use caution when you plan your garden bed design. The only fertilizer I use is organic seaweed extract. My folks practiced organic gardening where I am for 50+ years before I moved here so I continue to honor their commitment. Choose your own method based on your own convictions.

Have patience. Your garden won't reach it's full potential in a year or even 3 years. Plants know what to do and when, so you'll need to plan on making adjustments as they grow.

Consider winter sowing perennial plants, shrubs & trees from seed rather than buying them from local nurseries if your situation permits it. There's a Gardenweb winter sowing forum on this website that will guide you on how to do it. FYI--I gathered seeds from a neighbor's spirea shrub 5 years ago and this year the shrub is more than 3 ft. in diameter and covered in blooms.

Read & research. There are hundreds of good reference books available at your local library that will help guide you as well as warn you about pitfalls.

I wish you the best of luck & success.

There is so much great advice from everyone ! I just wanted to say what a beautiful space you have to work with! Good luck !!

You may want to get cardboard boxes at your local bike shop. The boxes are large and clean. Have fun planting!

Here's a quick idea. Climbing vines on the arbor, shrubs against the fence and a large garden bed with a bird bath. You could have a path between shrubs on the right and the bird bath garden. Hope this helps : )

ETA: My pink roses and purple clematis may not work in your area...but very cheerful. LOL I didn't add color to the rest of the beds, since that really would have been even more distracting.

lavender_lass reminded me to mention one other idea: when I planned my garden beds, I included what's considered 'hardscaping.' I included a granite walkway as well as a granite bench and patio. Plants aren't the only things your garden will feature when it's mature. I drove to a nearby quarry where I purchased the granite and hired skilled migrant workers to set my granite paths. The fence is part of your garden scene; the bench in the above photo is another example of hardscaping.

And to add to hardscaping info . . . if possible, do it first. Once plants are in, it's more difficult to add hardscape without damaging plants. It can be done after planting in some cases, but it's easier to do the hardscape when you don't have to worry about damaging plants.

That was some of the first advice I got, years back, about planning a garden ... plan around the big things first ... large plants like shrubs and roses, as well as decor like trellises, benches, pathways. Get the layout with the big things in first ... and then you can begin to fill in the spaces around with smaller plants.

In the cases where I have followed this advice and done this, I have really enjoyed the effect even though it can take several years to really mature. In the cases where I have not had the patience to do this (lol), I have usually ended up having to redo the garden several times to add things later, moving plants around etc. I find that to be much more work, and more frustrating.

There are many ways to plan a garden, but I agree with the suggestion to try and get most, if not all, of your hardscaping and larger things planned and planted first :)