There's a
big thread about this in the Leaf forum that you might want to review.
As far as power, most off-the-shelf EVSEs deliver 30amps, and most commercial buildings would have 208v service, so that's a max power draw of 6.2kw. It's important to remember that's a maximum value, though, as many EVs, like older/cheaper Leafs and Volts and Plug-in Priuses will only draw about half of that.
As far as which EVSE to go with, that really depends on a number of things. The first question would be whether it'll be free or paid. As much as I'd like to charge for free at work, I'd recommend you go with paid ($.50-$1/hr is reasonable I think), and charge for time plugged in, not just time charging. That way you keep out the people who'll plug in their plug-in-priuses all day and reserve the spots for people who actually need to charge. Plus you won't get resentment from all those drivers of gas-guzzlers at your work because you're "fueling up" for free.
If you do go with a paid EVSE, I think Chargepoint is probably the best bet. I'd avoid Blink or whatever it becomes at all cost. For a non-paid "dumb" EVSE, CC is always a good choice.
I'd also second Mike's suggestion that a bunch of 120v outlets and a "BYO EVSE" policy could be a great solution, although if going that route you could possibly try for 240v outlets instead (or in addition.) A bank of L6-20s would require the exact same wire/labor as a bank of 120v outlets, just with different breakers and receptacles. A bunch of RV-style 50 amp 14-50s would be even better, of course.