Oakes
I have done a bit of kayak ocean fishing in the past and hope some of this info helps.
Go the SIT ON kayak for open water. as you will find it hard to get in and out of a SIT IN.
PFD for open water is a given, also some water, an anchor ( something for a small tiny will do ), a leash for your paddle, a dive knife, some flares and a mobile in a waterproof bag at the least.
Also a MUST is a kayak with a rudder. The wind can push a yak all over the place.
Some good brand kayaks for this would be
- Malibu Kayaks
- Viking Kayaks
- Ocean Kayak
The above 3 are all plastic moulded
And for an Awsome fiberglass kayak you can't go past a Stealth.
These are pretty fast over long distances.
Perth beaches to rotto from memory thats a fair hike (an hour paddle at least) so make sure you have your witts about you. Also It aint easy getting a yak out when its 3 foot or bigger. But it can be done.
Triple check all weather reports before you go.
Nothing worse than paddling into a 20 - 25 knot head wind

(yes I have had this happen, not fun.
You could also look at the Hobie kayaks with a foot pedal propulsion but these things are way to to hard to get in and out of surf zones with.
Mate this way would be pretty hard going. IMO I would go something like a second hand rubber duckie surf boat and a 25 hp on the back. But that's just me.
If you do go the Yak option hope it goes well.