Hi Cecilia,
1. Does it get to full speed when you push the button all the way? If it does and gets there suddenly an adjustment should fix it, but if it never gets fast it isn't the foot controller at all. There are two strips of copper which bridge when you push it down all the way, bypassing the FC. If it's bridged and still slow, I'd be disconnecting the drive belt and testing again. If it still doesn't go full speed there is a problem with your motor. If it does, your belt is too tight or the machine needs lube.
2. The stitches should be excellent. As unlikely as it sounds, I'd check the hook timing. It's the primary candidate for this set of issues.
3. See 2. The needle could be hitting something "down there".