Re the deferment, you don't have to start your child in Primary education until the August after they are five. However, for deferrment, only children born after February of the year they could start school have the right to deferrement or not. If your child is born before that then the nursery have to apply to the council for the funding for an extra year and make a case for the child's deferrement.
It may be getting late now to defer with a funded place, but still possible, definitely try to get the nursery place organised sooner rather than later as the whole deferrment process starts now.
I deferred my LO, started the process in November and heard it was accepted the following March.
Most popular schools are over-subscribed and often have large class sizes and are pushed for space, so it might be worthwhile considering less popular schools which have reasonable reports, there are some rather out of date reports on the HMIE website, which might help.