need some advice
 

2000 x5 4.4. changing water pump. how hard is the job on a scale of 1-10?
change the thermostat as well?
dealer antifreeze?
any special tools needed when doing the replacement?

It would depend on your mechanical ability. It would be a 4 for me, but my could mean a 10 for others.

There are quite a few things that need to come out in order to do the water pump. You need a special tool that attaches to the fan clutch to remove it and such. If you are doing the water pump, you are already in there, so might as well do the thermostat. And yes, use factory antifreeze.

Hope that helps.