dydx,
First, welcome to RCU. You'll get a lot of decent advice from friendly people.

OK, Range: expect 1/2 to 1 mile from most standard radio equipment today. I haven't noticed any impact by losing sight of the plane. (I've recovered when going down behind trees, but you have to be lucky! ) As for weather, if the plane was water-proofed to prevent the electronics from getting wet, and you had a method to keep the transmitter dry, weather shouldn't be an issue.

Radio packages: virtually every transmitter (Tx) comes with 3 or 4 servos, one receiver (Rx), battery packs for Tx and Rx, and slow charger, a switch harness, and one servo extension. As has been said, you can buy stuff separately as well.

Not sure what frequency is used in Australia, but someone will chime in.

Engines only come with a muffler and a glow plug, but not all engines even come with those. Make sure you know what you're buying. That being said, if you buy an Almost Ready to Fly (ARF) trainer, or a kit, they usually will have the fuel tank, wheels, and control hardware. You will need to buy fuel tubing, as well as all the related equipment for starting and running the engine. (Fuel pump, glow plug ignitor & charger. A 12 volt starter is a good idea, but not absolutely necessary.)

There's really no "cheap" way to buy glow fuel except shopping around. If you're lucky enough to find a club or group of guys that buys in bulk, that's certainly cheapest.

Engine size: As was mentioned, kits or ARF's will have a recommended range of engine sizes. I recommend buying one at the top end of the recommended range. .46 two stroke, or .52 four stroke is about right for the typical "40" size trainer.

Flying time: as pkh said, depends on some things. Typical 40 size trainer ARF or kit, will usually have either an 8 or 10 ounce tank, and give 10 to 15 minutes flight time with a 46 size two stroke. A 52 four stroke would get you closer to 20 minutes on that smae fuel.

The battery pack that come with your Rx (600 mAH) will get you about four 10 to 15 minute flights before recharging, but it's recommended that you check the pack's voltage between flights with an "Expanded Scale Voltmeter" (ESV), which is a tester that puts a load on the pack for a truer reading. (Can be bought for about $15 U.S. at a hobby shop.)

The Tx pack will likely last for a full days flying.

Larger capacity packs and larger tanks will extend flight times of course.

Feel free to ask questions.
Dennis-