Hey man - Just wanted to stop by and say what a lovely motor you've got... it's absolutely identical to mine haha! I've also got one of these MP3's in the same colour, cracking cars. I know that you posted this thread back in March but I just thought I would say hello :)
I've noticed the one you got was for sale back in January time by the same trader that you probably purchased from, I had my eye on this one and the one I've got now - I was going to view this one but I viewed the one I purchased first and just had to have it. Mines on a 52 plate and currently on just under 76K.
With regards to the twitchy fuel & temperature gauge when the engine is off, this is actually caused by the instrument cluster itself and after a few years the soldering inside of the cluster becomes weak on the circuit board and causes this exact symptom - it appears to be a common problem on the MK1 Focus's (my original MK1.5 Zetec also had this) but when the car is running the gauges work fine. The only way to fix this is to remove the cluster and re-solder the required places and it should fix it. Or if you haven't got the equipment or the time like me, just purchase a new cluster (though I haven't bothered to as the issue doesn't bother me too much).
Also keep an eye on the Electric windows, I discovered when I got mine that on the way home after picking it up, one of the rubber holders on the regulator that holds the window had totally come out of place due to the bolt becoming loose and the window wouldn't go up properly. As I was unaware of this at the time I just purchased a new regulator but I think that in the end it only needed the old bolt on the old regulator tightening up as the original regulator still looked intact and working.
The only thing that bothers me slightly with mine is the fuel consumption, on a good week I'm only averaging 31-34MPG (120 ish miles to £25 worth of fuel) at the very best and that's keeping the gear changes below 3000rpm. Though I think mine could do with an oil change right about now personally. How are you finding the fuel economy on yours mate?