I did the opposite to Aris
1 transmitter, 1 receiver. Then everything is slaved off that.
Pluses:
1. It's cheap
2. It's simple - just attach the receiver to your primary flash unit and set all the others to 'slave'
3. You don't have to worry about making sure you have a receiver per flash
Minuses:
1. Sucks at events where other people are using flashes - everytime their's goes off, so do all your lights
2. When using very low power from the main flash, the slaves don't pick up that flash reliably and fail to fire
I don't do much event photography, so having a receiver per-flash hasn't been a problem (yet). I'm about to do an event this weekend, and am wondering if I should dash out and get three receivers so I can 'un-slave' my slaves and have them all trigged via the remote instead of any-old-ambient-flashes.
In my stuff in the studio, it hasn't been an issue at all, except where I've wanted to really, really reduce the power of the primary light (to use a wider aperture, for example). I did a cheap hack and bought an ND filter instead (allowing me to up the output of the flash to reliably fire the slaves, and allow me to still use a big aperture), but it's a bit of a hack really.
I would get the extra transceivers as and when you can, but to save cash for now, you only need a transmit/receive pairing, and could slave the rest.
And yes, you'll need a transceiver-to-hot-shoe adaptor per flash, unless your flashes have PC inputs (not many do these days it seems).
Now I've said all that, you could go the SUPER cheap way and get a hotshoe extension cord to one flash, and slave the rest.