Wow... Use the force Neta..
Suggestion: Try not starting as the Byzantine Empire first off. Try maybe a count in Ireland or anywhere in the British Isles first off. It's a tad easier for a beginner to learn and build up a realm rather than starting large. Maybe a Viking Ruler as they have easy Conquest CBs etc.. Either way, try starting small and build up. Learning how to manage vassals is easier if you don't have that many. Laws, CA and creating/distributing titles what they are and the best combinations to have. The game is not something you'll master quickly and it'll take quite a few play throughs before you really get a grasp of it and then, give the Byzzies a go. They're not that difficult but you need to be on top of the mechanics of the game or it'll fall apart pretty quickly. Timing is everything so a little patience is required.
1. Then the character is not independent if it's showing red. His Character portrait will show who his/her Liege Lord is so to declare a war you'll need to declare war on the liege lord if they're not independent.
2. Gold helps or hover your mouse over his opinion of you and see what he wants. It may be a vassal he wants or a new title. Or he just may be ambitious so not a lot you can do.
3. The units will show up in game after purchase though not sure about saved games. I don't get the music DLCs so I can't answer that.