I went ahead and ordered PCBs and assembly from JLCPCB.  There was a little more friction to the process than I had hoped.

The service is picky about the formats for the BOM and placement files, and it seems some parts that looked available on LCSC were actually not available for the assembly service, so I had to select other ones.  I would recommend that if you intend to use this, you start from the "Basic" parts library.  Because I didn't, I also had a good number of special parts that added cost to my order.  Oh well, lesson learned.

Unfortunately the position data for assembly exported from KiCad also couldn't be directly ingested by JLCPCB, it took some manual massaging in a spreadsheet to get it right.

But in the end, getting 5 prototype PCBs produced, fully SMT assembled and shipped for about $72 is still a very good deal!