First:
calling dbSyncRate(0) does mean that Darksdk will decide how fast to refresh the screen/it will try the max syncrate possible. you should be able to use any sprites as normal.. if you worry about movement speed, then just use a timer approach for real time speed calculations...
Second:
cant help on that, you may need to post the file, and the code that produces this behaviour.
Third:
As you only need to specify an image once for a sprite, you should be able to do it by playAnimationToImage... and then it should just work.
-- I just started with DarkSDK, by translating DBP Projects. --