It probably is obvious or perhaps seems silly at this time, but remember to include appreciation potential in your parameters. As long as you are going to be a landlord you might as well make an educated guess as to the upside of what you are buying. This could include finding the stomach for an area that might include some grief. It might mean staying in nicer areas but researching planning and zoning agendas or just studying trends as you have mentioned.
I knwo you are thinking Los Angeles but I think San Diego also has a lot of potential to develop some of the surface streets for more High rise rental/mixed use capacity. The most obvious seems to be El Cajon Blvd. Clairemont Mesa BLVD seems good too.Maybe Genesee. These are just examples. I could see these becoming something like Wilshire Blvd. in Los Angeles. Thinking about the surrounding areas for rentals may have some increased benefit in future rents or appreciation. This may never happen or take a very long time. It seems like potentially worthy food for thought.
As far as buying a bigger building. They are not all handled by syndicates. You can buy whatever you have the dough for, although you probably would incorporate. I can’t really address your possibilities there for lack of practical experience. The SDCIA blog is a good source of info on this topic.