Have you tried earplugs to cut down on the noise of the snoring? I have to wear them all the time with my partner. They're uncomfortable at first, but you get used to them.
Do you have a fan for when it's hot? I find a wet face cloth on my forehead while the fan is on cools me down enough to sleep in many instances. Quickly jumping under the shower to cool down can help too.
You're already going to bed and getting up at regular times, which is important. Some sites I've checked out recommend only going to bed when you're tired, though. If you find you're tossing and turning and not at all sleepy they say you should get up and do something relaxing until you're tired and ready for sleep.
Have you considered getting a meditation tape to help relax before sleep? They may help your brain unwind, which could work wonders since it sounds like it's mostly the stress that's keeping you awake. I find my hypnosis MP3s really good for that. They're not meant to put me to sleep, but the moment they say 'relax' I get a little too relaxed and start dozing!
How much exercise are you getting per day? Exercise is supposed to help regulate sleep. However if you do it too close to bed-time it can keep you awake. A bath before bed can help your body and mind relax so it might be worth trying.
I've heard that a small snack of carbs with a little protein before bed can help too. They work together to boost serotonin levels, which converts to melatonin to help you sleep. Something like a banana and a small glass of milk for instance. As long as it's not putting you over your daily calorie intake it might be worth a shot. However I think this only works if your melatonin is low to start off with. Still, it's worth a try!
As to being woken at 4.30am... the only solution I found to this one is to sleep in the spare room I'm afraid.