After using the first 3 pre-ordered FP+ in one of the parks (e.g. MK), is it possible to hop to another park (e.g. EP) and choose additional FP+ for the the other park? and than hop to a third park (HS) and choose additional FP+ for this park and at the end of the day go back to the first park and choose another FP+ in it?
Yes, 4th, 5th, 6th, etc FPS can be in any park. As soon as you tape in for your 3rd, you can book a 4th in any park, before hopping.