A: No. You do not need to live separately before filing for divorce in Florida. You also do not need to live separately during the divorce if you can safely live together. One of you has to be a resident of Florida for 6 months and the marriage is "irretrievably broken" which means there is no need to prove anyone is at fault; it means you no longer want to be married and there is no possibility or reconciling.
A: The cost of a divorce depends upon the amount of time it takes to divorce and the attorney's hourly rate. If you and your divorcing spouse agree on many things then the process will go more quickly and cost less. If you or your soon to be ex fight and cannot agree it will take longer and will cost more. Yes, some attorneys make arrangements for payment plans and in some cases you may be able to get the court to award attorney fees to you from your spouse.
A: I would not wait. If you were to get his pension upon his remarriage before your child graduated from high school and there is a final judgment and a signed agreement, and those are the facts. You should ask him to sign over the pension. If he does not you should move to enforce the final judgment. I would not wait. He should not be able to change the conditions of the final judgment; in other words put the pension in his Will. If you wait until he passes then you are possibly having the same fight.