Hi Alan,
Wow what a price for flights via Virgin, personally I would book your villa and then start looking for flights. Throughout the year airlines do have offers and that is the time to book. Also indirect flights are nothing to worry about you do clear customs in the first airport and once you arrive in Orlando all you have to do is collect your luggage and off you go and we have often travelled with our grandchildren on indirect flights and have never found it a problem. Charter flights into Sanford is also another option. Most of the larger airlines offer a reasonable luggage allowance and it is not the out flight that luggage is a problem but the return when you have exhausted all the Malls.
Val