You are definitely entitled to have a copy of your records and radiographs, though the dentist is permitted to make a reasonable admin charge for photocopying etc. Copying non-digital radiographs is a bit more difficult but your new dentist could ask for sight of them from your old practice, (even though you haven't actually seen the new one yet).
I'm retired now but I can barely think of more than one instance in 35 years where I wanted to see someone's previous records - we start with a blank sheet of paper each time and it's easier that way. Perhaps reviewing radiographs might be a little more valuable in a small number of cases.
Regarding notice of the change: the new practice owner would have stipulated that the retiring dentist should not inform the patients in advance (standard Sale and Purchase Agreement) to maintain the value of the goodwill. Chances are the staff only found out on the day the contracts were signed. The more notice the patient has the more time they have to seek out a different dentist somewhere else eg on recommendation from friends, as they have no particular reason to stay 'loyal' to the location if their favourite old chap/chapesse is no longer there.
I wouldn't recommend taking it out on the new chap - he might be brilliant and you'd be cutting off your nose to spite your face. Give him one chance, at least. Your unhappiness is not his fault, it's just the way things are done to protect his interests - in the sale of a Practice the value is far and away the most important thing for both sides. (The patients are a side issue, though keeping them happy becomes more important for the new guy as time goes by). Which is where my successor struggles, but that's a different story