I forgot to add that MH has its own shopping district and some of the sidewalks there are 4-5′ wide with tree easements. It also has small groceries and other small biz interspersed in a couple of different areas (walkable by its residents) and is situated just 3 miles from Lindbergh Field (SD airport). You will CERTAINLY find a 7K sf lot and even a 12K sf (corner) lot but alley access on many of MH’s lots makes a smaller lot feel more usable. MH DOES have 1/2 to 1 AC lots above the Presidio but I fear any listings in this area may be out of your price range unless you are willing to do major work on the place (not even sure if there are any “fixer” properties left around there).
Unfortunately, the large lot you desire combined with the nearby urban amenities you desire isn’t very doable in SoCal except possibly in BH, like you previously mentioned that you considered but your price range makes all of your desires in one pkg a bit challenging.