The outdoor structure is attached to the house as part of the roof. Removing it will change the roof structure and incur a large expense. U can update the posts but those type are very common here in Southern California. U can paint white and add cone lights to the bottom to give more light. For your yard I believe in using space for whatever u need it. Seating areas are great u can always buy a bar if u don’t want to build one in. Matching your pavement is going to be a challenge because that pavement is from the 60s. I do see play equipment. You could do synthetic if u don’t have a dog and u can always put chairs and a bar on synthetic. Also it is unsafe to put a charcoal grill under a structure. We have to put in vent hoods if we put a grill in and our grills are gas not charcoal.

To me tall planters are a bit off for the site but big ones for sure and try to fill with seasonalplantings to enjoy the fire pit as laong as possible . There are some really cool prfab bridges you might want to check out to avoid the machines . The path IMO should be done with the same stones as the firpit too many different things make for poor design nad aldo the steps the same stone it ales a bit more work but really the best way to handle stone work in different places .

I would put trellises on the fencing and plant climbing, flowering plants. I would also put lots of containers on the concrete pads to plant grasses and/or flowers:

Yep, I have gravel gardens...which I love because I live in the driest part of the UK and grow a lot of drought-resistant perennials for a Mediterranean climate. But no, it absolutely is not low maintenance. A sharp hoe makes short work of weeds in my usual beds...but in the gravel gardens, I have to hand-pull every single weedling (and on a public allotment, there are millions). I did try using a landscape membrane underneath but that workd out worse than useless. Within a couple of seasons, blown in soil particles had migrated into the gravel which then made a perfect substrate for even more weeds...which then grow through the landscape membrane. The whole thing had to be removed...which took me the best part of a decade. So if you do use a rock mulch, try to avoid underlying membranes. There might, conceivably be a use in pathways...which can be given an annual herbicide treatment but around existing plants...nope. Having said that, grasses, succulents, evergreen subshrubs and bulbs all do tremendously well...ad with a fill-in of the likes of eschscholzias, nemophila, platystemon, aurinia and sedums, the beds are really very lovely. I adore my gravel gardens intensely and am prepared to put in the continuous effort required to look good (alpines and other rockery plants such as lewisias,edraianthus, saxefrage and calandrinas) do well with the free-draining, warm substrate too