It all depends on your question really. DC and cancer cell cultures can work very well in multiple settings. Easiest would be to use a flat 96 well plate with roughly 30000 DCs and depending on the size of the cancer cell lines used see what works. However, it all depends what you want to see. If it's cancer cell effect on DCs a 1:1 ratio should be fine. If it is antigen uptake then you might want to irradiate the cancer cells.
For murine DCs I would make a preparation of DCs derived from bone marrow. You can find many protocols online for this. They are called BMDCs.
For lung cancer cell lines, I would use LLC or CMT-167 (lewis lung, or carcinoma)
Secondly, what is your final read-out? If it is, flowcytometry you will need a good amount of cells while for other assays you could use the 96 well plate. As suggested by Eytan, around 50.000 cells total (1:1 ratio DCs:cancer cells) should be enough as first try.
The ratio of DCs/cancer cells can also vary depending on the type of assays you are doing. You need to provide some more details regarding this.