Too Fast congrats for keeping trying! Possibly the reason for the tardiness in trying to reply to your questions is, because this is FR, that it is all a bit complicated and it depends what deal you are on, where you are based, whether you are flavour of the month, etc.
What you need to concentrate on more is that part of 5/4/5/4 involves accepting that you can be put on 5/3/5/3 when your employer deems it necessary. Also, some of the "4" days are not actually days off, but part of your leave - around 7 of minimum legal entitlement - if memory serves me correctly. All other leave is used to make up your 4th "day off". (Did anyone mention these little bits .....??). So if you are trying to make this work for you, be sure that your best plans will be thwarted.
At least you are having the wit to ask before you get in and discover the realities. Smoke, mirrors, uncertainty, marketing, propaganda, manipulation - that's the name of the game.