A softbox is a must with a grid fitted as its more directional than one without and definitely so with a brolly. Also depending on what you are doing you will need grids/flags as you have to control the light even more. A W/B card is a must as you will no doubt get colour cast.
Radio triggers are the best route to go down. You don't have to go down the PW route as you can purchase cheaper triggers like this.http://cgi.ebay.co.uk/Speedlight-str...item2ea9a020fa
and they also work great with off camera flashes. They are good as i have and still use them. The main difference between them is that the PW have a better working distance.
Safety is a must as people easily trip over the wires and stands getting knocked and the light smashing your model in the head. I know
You don't have to go mad with the lighting at first you can get good second hand gear like Bowen or something like the D-lite kit. The light modifiers are not cheap and again you can get second hand or cheaper versions, but they are a must.
With some things you can make your own modifiers.

Look forward to seeing some images.