Blanc, the number of hives you need depends on what you plan to do with your bee's to make a living, I have a friend that has 100-200 hives that sale's 200 nucs and 100 queens, he sales very little honey, he build's and sale's his own equipment (hive components) and does removals, he works year around mostly alone and mostly winters around 100 hives a year but builds up early spring close to 200. I have other friends that pollinate and have 500-1000 hives, they sale honey, queens, nuc's, pollen, wax, ect., and has workers working for them, what you need to figure out is what it is you want to do with the hives to make a living then that would help you with the number you need. just my 2 cent worth.
i think at least 400 if you are going to plan on honey being the primary product but as few as 150 if you sell nucs/packages/queens as well as honey.
all you guys quoting what a drum of honey goes for would be shocked by what we sold it for in the late 70's early 80's. if i remember right we got about .65/pound back then.
finski is right about working with a commercial beekeeper. it not only takes a lot of work but also a lot of equipment.