The Luminex system is only up to about 60-70 multiplex at this point and keeping in the 20 range is the best for realistic assay design and optimization.
The Luminex system is much less expensive than a FACS instrument and the learning curve is much faster. Although, if you already have a FACS or plan on it using it for other purposes, you could test the Luminex technology on that first before commiting. I never tried to do a multiplexing Luminex assay on a FACS instrument, but if you get beads of highly different dye content, you might be able to gate on the populations and pull it off.
Avocado_man