Gearbox oil change - probably a good idea if you have no history of it being done. Sele makes no difference at all, you just drain it from the bottom and fill it till it reaches the fill plug like most gearboxes. Drain plug is a little tricky to get to, you need a cut down 12mm allen key. Fill plug on front of box casing, simple. Just make sure you get the right oil.
Air filter is a bit tricky in that it's 20 mins work not 5 mins like some cars. Take the main inlet hose off the MAF and push it away to one side. Disconnect the wiring plug to the MAF. Unbolt the relay holder off the front of the battery tray and push that away too. Then you just need to undo the 3 screws that hold the airbox lid on. These can rust or sieze or strip but being in Aus yours will hopefully be fine. Then just wiggle the airbox lid out, pull out the old filter, vacuum any rubbish out of the bottom of the airbox, and refit everything. Easy.
Cambelt and associated gubbins pretty straightforward, if long winded. Spark plugs only need changing every 100,000km and they're not cheap so don't rush into that.