5 My horse’s feet chip and fall apart without shoes. Won’t he get worse if I keep him unshod?

This will depend on whether your horse’s feet chip because they are too long or whether there is some sort of dietary issue that is causing the horse to grow poor quality hoof horn. Natural hoof care practitioners put a rounded bevel (mustang roll) around the outer edge of the hoof wall, this helps prevent the chipping that can happen when the hoof wall is rasped flat.
Many horses have a sensitivity to certain grasses or prepared feeds. This can cause an intestinal upset which then has a negative effect on hoof health and can cause anything from chipping and splitting of the hoof wall, thrushy frogs, whiteline separation to laminitis.

6 What is the transition period people talk about? Does it mean I won’t be able to ride my horse for a while if I take his shoes off and go ‘barefoot’?

The transition period is the time it takes for a recently de-shod horse with unhealthy or unsound feet to grow strong healthy hooves and return to soundness. The length of transition will vary between individuals. The speed of transition can depend on the health of the horse, and its immune system, whether its lameness issues have been long term or a recent event, the horse’s diet, lifestyle, how much daily movement it gets and of course regular trimming.
As in question 2, how soon you can ride your horse will depend on his hoof status, whether he needs hoof boots to be comfortable for riding and how much you, as the owner, are willing to help speed up your horse’s transition by making any necessary changes to his lifestyle, feed, movement etc.
Some horses though take 30 minutes to transition from shod to barefoot - the time it takes to remove the shoes and trim the horse! Others may always need the protection of hoof boots when ridden on gravel etc but all horses, ponies and donkeys should show an improvement in hoof health/soundness at the end of their transition period.