I have had the same experiences and recommend the following with all my heart:
1)Listen to this podcast from Ari Tuckman and read his work on children lying - it will really help you understand where they´re coming from
https://takecontroladhd.com/podcast/426 He was written extensively about it too. I recommend all parents read his work in fact!
2) Leaving a book as opposed to access to the remote is a good idea as is training him to understand he cannot leave his room except for the loo. You can praise him for doing so as you have a camera. The reason I say this is that later on he will eat your cupboards bare and access all the devices around the house when he´s older. It would be good for him to try to vocalise what his sleep patterns are and what is driving him.
3)It appears that rewards are not enough to change his behaviour which will just mean you will need to up the rewards continuously. He may be driven by impulsive behaviour and a need for stimulation when his own levels of dopamine are depleted. That may (nor may not be) driven by ADHD. I would talk to his teachers about his concentration and self control capacity vs the rest of the class. Can he focus only when he´s interested in something? What is his boredom threshold like vs the rest of the class. V low boredom tolerance is a key symptom. It may just be a passing phase that has become a habit but I think the sweets stealing is a sign that he wants more attention, at all costs, so even if it´s negative. His behaviour is probably symptomatic of a need for a deeper connection with you. If you can carve out 1:1 time for 10 mins (put stopwatch on to avoid tears) on his terms (he chooses) it may subside.
4) Calmer Easier Happier Parenting by Noel Janis Norton covers all of the above and her methods are incorporated into The Parent Practice´s courses (Elaine Halligan, the director, is on this forum). I actually hired Noel for some issues and she fixed a multitude of problems via telephone consultations. PM me if you need further references or a transcript from one of Ari Tuckman´s webinars I have on file.