Not to discourage other answers, but while you're waiting, you might find these threads interesting:
What were the main factors in the decline and fall of the Byzantine Empire? - /u/shlin28 addresses some misconceptions that the OP had regarding the decline
AMA - Byzantine Empire - there's a lot of handy general Byzantine info in this AMA featuring /u/Ambarenya, /u/Porphyrius and (everyone over at /r/BadHistory's favorite poster) /u/ByzantineBasileus
I hope that helps!