I'd agree with Steve on all counts. No matter what brand you're using, the light meter will be helpful in getting those exposures right.
So other than the light meter and a good editing program, I'd consider looking into some good books on lighting. This is a great one:
http://www.amazon.com/Master-Lightin...ef=pd_sim_b_16
This one's also a favorite of mine:
http://www.amazon.com/Photographing-...4517603&sr=1-1
This one I like for beginning lighting:
http://www.amazon.com/Beginners-Guid...517693&sr=1-11
You can do a lot with the three lights you have. Once you get that down, only then would I think about investing in more equipment. Good luck!