You're first board purchase sucks. You know next to nothing about what you are buying from someone possibly desperate to sell it and then you're going to grow out of it in only a few short months. Yay. Then you've got to try and sell it, which can even be impossible.
But the really good news is you've definitely come to the right place.

I reckon you're ready for a short, but wide board. Especially if you can already tack and gybe a longboard.
I'm going to stick my neck out here and say the first place you're going to go with windsurfing is "freeriding". That is sailing out and back, fancy gybes etc. You really just
have to start there.
I also recommend a Starboard GO, or similar (like what?). Something around 140-150 litres and you can both learn on it and use it for years. Eventually you'll get something smaller to blast around on but you'll still likely pull out the old Go when the wind's light (every 2nd weekend), or you want a platform for freestyle practise, or something to teach another beginner on. I wish I'd bought one.
Something like that might cost a little extra, if you can find one, but you'll absolutely get your money's worth out of it. What's the saying? - don't save a dollar and end up paying twice. Besides, they hold their value well.
You can pick up a decent 2nd hand rig for around $600, even brand new (08 gear) for double that, $200- $300 hundred more for accessories like harness and wetsuit etc. I found a 5.7m sail was perfect for my first year. Remember: you want a "camless freeride" sail.
Watch the buy and sell section on this site like a hawk, occasionally a genuine steal comes on. This is a good buy but I'm concerned you'll bust the deck up learning to get into the straps and harness (catapults), the Starboard GO has a forgiving EVA deck.
www.seabreeze.com.au/Classifieds/Windsurfing/Boards/~zxqq/2008-Fanatic-Shark-268-cm-160-litres.aspx?search=iVVAl2umBXmHLC7VP1FIeA%3d%3dHere's the GO:
http://www.star-board.com/2008/pages/products/v_go.phpAgain, you've come to the right place. Post a question you'll get a dozen answers.
Oh yeah, and don't be shy to ask someone at the beach if you've rigged properly. 2cm here and there can make sailing 2x as easy. Very important to progressing quickly.
Welcome aboard.
PS If you were on the Gold Coast you could borrow my old soviet tanker of a board and crusty old rig, but I've already lent it out.