It's unclear if you want advice on plants. If so, we'd need to know what zone you live in.
We just put in a big flower garden (300 sq ft) in an area that was previously a weed jungle. We have paths, a handmade swing with a pergola roof, and four separate sections of plants (orange tree area, butterfly garden, fountain + shrubs, and swing area with shrubs, vines, and annuals). This is phase 1 of the backyard renovation. Either this fall or next spring we'll double the size of the flower garden and add a water feature. My advice:
1) The most important thing to do is identify the weeds that you have and how they spread. For some, weedkiller might work to kill them; for others, maybe not.
2) Do the weeds reseed themselves, vine, or spread by rhizomes? We learned that the weeds with rhizomes needed to be dug up as much as possible; in the areas where my husband decided I had done enough and tilled, the weeds are coming back because enough of the rhizome survived.
3) We had previously used landscaping fabric, when that area was a vegetable garden. This worked well in certain areas and was a nightmare in others. As someone else said, if you put dirt on top of the fabric, the weeds will grow in that. Also, for me some of the weeds with rhizomes would grow under the fabric and actually manage to shoot up suckers through it.
4) We stripped the entire area to soil, with a mixture of mowing, weedkiller, raking, and digging up roots. So. Much. Digging.
5) After the weeds were vanquished, we spent time on grading the area appropriately, to make sure we had decent drainage. We didn't want water to pool in certain areas, especially against the house. Our area wasn't as huge as yours, and we did this ourselves with a few bags of dirt and a rake.
6) I spent more money to buy larger plants instead of seedlings. It looks nicer to start with, plus it helps keep the weeds down, because there isn't as much open space for them to grow in.
7) Lots of mulch. Lots and lots.
8) I don't have the time to babysit plants, so I chose primarily native plants or those that are well-adapted to the area. I chose perennials in all but a small area.
It took us about 2-3x as long as we estimated to put our flower garden in, and we did a lot smaller area than you are planning. Be cautious about buying all your plants upfront if it might take a while to get to planting them.