I haven't read all the post however I agree waiting 3 years is far to long to wait to move as your daughter would be entering a school knowing no other child. Depending how confident she is could leave her open to feeling alone. Apart from that if you can wait 3 years I assume you're not unhappy.
I've not left the UK although heading to Australia soon. Unfortunately over the last seven years the UK has changed massively. For example food and house prices are far out of control and everybody I've spoke to say there better off in Australia, although I'm guessing it's not just the cost of living over there.
The other thing to bare in mind is you remember the UK when you was there, do you want to come back because you have good memories because that's what they are memories. All the people you knew would be different the shops pubs etc closed, moved or closed down.
A lot think the grass is always greener somewhere else but often this is not the case.
Could you not come to the UK on a holiday before making such a big choice