Preparing the BMW X5

What, I ask myself, should i be doing to this car in preparation for this trip?

Tyres
I know it needs new tyres, I've been putting it of as long as possible so that they will be as fresh as possible when we set off. What tyres will I get? When we bought the X5 it was running Michelin tyres. I had to replace two due to an unrepairable puncture of one (isn't that always the way) and I bought Bridgestones. The Bridgestones are all but worn out, the Michelins are still hanging on - I estimate that the Michelins have done 90k, the Bridgestones 40K.

We are not planning on too many dirt roads, maybe ones out to the big attractions, well used, frequently travelled type ones, so highway tyres should be good.

So, I'm going to buy a new set of Michelins I'd reckon.

Spare Wheel/Tyre
Do we need to carry more that the one spare for either the car or the van (duel axle)? I have spare rims and tyres and could take them, but they would have to travel on a roof rack / basket and I wonder how safe they are from either working loose and falling off, or disappearing in the night and going to someone else's home.

I'm keeping my options open on this. I could probably fit a second spare to the rear bar of the van, but I'm already concerned about overloading - start early with the worry, cull anything that isn't necessary. The car is registered to tow 2700kg, the van has a tare of 1660kg and 450kg load making 2110kg total, and I'd be comfortable with that.

Anyone have any comments regarding wheels / tyres?