From a 747-400 pilot.
Low power used to start roll, minimum to prevent blast damage behind. Once rolling, idle power is usually enough with occasional low power applied to keep moving. Resistance to motion is very dependant on weight and slope of taxiway- they are often not flat!
A hard 90 degree turn should be at about 10 kts, a more gentle one can be at up to about 15kts.
Switching on the fuel cut-off switches during autostart will apply fuel at the correct rotation speed automatically, not when you put the fuel cut-off switches on. The autostart will monitor itself and cut-off the fuel if any parameters are not correct, and even re-apply fuel. I wish we had it on the latest 737NG!
(Don't apologise for your English! Most English people can't write English as well as that!)