I am using DMEM + 10% FBS and 6 day old BMDCs in my experiment which is done using a 24 well plate. I will use the cells to make western blot samples, both cell lysates and supernatants will be used.
If you are using 24-well plate for your further experiment then 1-2 million cells per ml would be fine. In 96-well format 0.2-0.4 million cells in 200 ul should be ok.
I use 96-well plate for maturation of BMDCs and later use cytokines and maturation markers by FACS. These cell numbers work fine for me so I think it should be ok for your experiment.