In close to the island where the reef runs, be mega-careful. In a heavy swell you can end up caught up somewhere you really don't wanna be. Just pick your days well and if in doubt, don't go too far beyond the channel.
However in a 5.2m runabout you're at a fair advantage, I see tinnys struggling along out there a fair bit.

As far as fish goes, any sand patch you find amongst the reef and weed is likely to be chockers with good sized sandies, the odd KG, and skippy if you anchor and burley hard.

 With GI/Carnac area I like to sit back and watch for a few minutes to see what the waters doing before I head out past the islands. Pay attention to your Gps and pick your days. I used to go out to the FFB regularly in my old boat (brooker 5mtr C/C) and as long as the weathers playing the game I had no problems.

Just be careful going through the channel between Garden and Carnac, gets a bit shallow in places so best to drop your speed back a bit and keep an eye out for rocks. Once you have some GPS tracks you be much more comfortable with it. I go out the back of the bank all the time in a 5.4 boat so you should be fine in a 5.2, sometimes in a big swell the waves really rise up sharply on the bank itself so just be wary if you fish the bank itself. Sepia depression is ok though and with the swell this weekend you should be ok - there is always a chance of a rogue wave rolling through though but I doubt you will get one breaking on the bank this weekend.

when you head out between carnac and gi jusyt observe the area about 3-5 ks out and see if there is any white water indicating waves are rolling on the bank,if they go out the back of carnac ito 20 odd metres of water and you should do fine on big sand whiting ans skippy. have a great day out guys.