So I have a RaspPi and it has an I2C exposed.

I would like to do some PWM on 8 sets of LED strips each is 0.5-2A @ 12V

I bought a bunch of MOSFETs rated 30W and some optoisolators (since the LEDs are on a different PSU to the RaspPi)

optoisolator: http://uk.farnell.com/jsp/search/productdetail.jsp?CMP=i-ddd7-00001003&sku=1045424

Now what I need is 8 i/o pins .. hence
http://www.farnell.com/datasheets/12170.pdf

I was planning to connect the pins directly from the io expander to the optoisolator. And on the remote side use the optoisolator to connect the MOSFET to +ve (see lower diagram here: http://letsmakerobots.com/files/userpics/u1533/BJT_vs_FET.jpg )

Now the question is: do I need any supplementary circuitry or do I just join the dots?