Not 100% true, im now running 9 speed with a 10 speed SLX clutched mech. Thanks to this forum, all it took was a 6mm spacer under the cable and it works perfectly.
CV grease from a car place, 1kg tub will outlast me. I use either that or copper grease for threads on my bike, bike specific products are just five times the price.
I always used to get my LBS to do headsets.
Then i just went for it myself with a screwdriver and a hammer, then a hammer and a lump of wood.
Wondered what i was so afraid off its a doddle as long as you take your time. Keep checking to make sure its straight.