There were enough annoyances (described here) in my design of the PCB that I decided to do another revision. In addition to those earlier -described annoyances, I thought of a few other improvements.

• I put a keepout for the ESP32 antenna area. No copper pour under that area on the back side, and not traces routed through it on the front side.
• The ESP32 module was hanging a couple of millimeters over the edge of the PCB. That didn't matter much, but it made creation of the enclosure slightly awkward (more about that later). I repositioned it to be fully within the PCB outline.
• The problem I had with the less expensive power connectors was just the size of the hole for the ground pin. The hole for the 12vdc pin was big enough, so I just replicated that hole and pad for the ground pin, the original (better but more expensive) connectors will still be fine because they have a couple of soldered mounting tabs and a plastic pin for stable placement. I also checked into a couple of no-name connectors, and they look like they will fit the same pair of holes.
• Rather than switch to one horizontal and one vertical orientation for each of the JST-SH and JST-PH connectors for I2C, I decided to remove half of them. I now have just one footprint for JST-SH and one for JST-PH, both horizontal insertion. I decided that anybody who wants to use multiples of each can just use a passive fan-out hub. Also, as expected, soldering the JST-SH SMT device is a pain in the neck. My decision of this was accelerated by the move westward of the ESP32 module. There's still enough room on the layout for both pairs of connectors, but it's pretty cramped.
• (previous) cap holes
• I changed the PCB mounting holes to 4mm and moved them a little bit further from the PCB corners. I also fixed the non-symmetrically-placed one.
• I changed the wrong footprint for the MOSFETs to be the correct TO-220. I also rotated the footprint 90 degrees so that they MOSFETs can be bent to lay on their backs (so to speak). That can reduce the overall height requirement for the enclosure since the MOSFETs are the tallest.
• I removed the two 0-ohm resistors coming from the power jack. In all my testing so far, the 12vdc power supply has been working just fine for the ESP32 module, so I guess the on-board power regulator is happy enough.
• I moved all of the connectors on the edges of the PCB closer or even beyond the edge. The enclosure template I am using has rounded corners, but that means I need to put a little gap between the enclosure walls and the PCB. The movement is not enough to cancel that out, but it makes things a little easier to work with.
• I tried various things to provide additional through-holes for the electrolytic capacitors, but I couldn't keep KiCad's design rules checker happy. This is due to my limited experience with KiCad. I decided to leave them as they were in the original revision.
• Placing the ESP32 module on the board was a really snug fit, so I slightly increased the hole size on the pads while keeping the copper the same.
• This isn't really a change to the layout, but I'm going to use standard 4-pin right angle headers for connecting the fans to the PCB. The vertical insertion was kind of awkward considering the dimensions of the enclosure. I haven't found any horizontal insertion fan connectors, and standard headers have the same pitch. I just have to be careful to have enough clearance since the thick part of the connector on the fan cable will face down when I use horizontal insertion. I didn't change the footprint on the PCB; it still shows the vertical insertion connectors.