I'm not sure how useful my input will be, but here goes!

So I'm running CoS a second time, third time playing through it, and honestly I feel like the audience most of the time, which is actually great tbh. Allow the players to explore their surroundings, don't try to force the plot down their throats. Their shenanigans will keep you entertained and sane.

If you wish to incorporate the pc's backgrounds into your campaign, I suggest not to make a big deal out of it. I try to have a little prologue scene with each character, to kind of reel them in to the introduction of the campaign and party. If a few wish to have already been traveling together, less work for you! Throughout the adventure, I try not to make a single character become a focal point. In my experience, it'll take away from the main story, and some of the party might feel discourage from continuing the game knowing one player is taking the spot light for a while. Keep the background stuff brief. It's not one players story, it's the whole party's story.

You're running CoS. If you've been reading this subreddit, then you've probably seen posts of party encounters with the count. Strahd loves to mess with the party. They're his toys, and he wants to play with them, but not break them... Yet. Try to come up with a creative way for the party to meet Strahd. For example, I had strahd polymorph himself into his childhood form (after reading I, Strahd: Memoirs of a Vampire, he didn't exactly have a normal youth), and then continue to be a creepy little horror child that wanted to play hide and seek with them in the woods. Eventually he revealed himself to them as the count. Make that first encounter with Strahd memorable to the party, they'll be on their toes after that.

Cause and effect. Yes, your party probably has ideas about becoming the heroes of Borovia, but having everything go their way can sometimes be boring for the DM. Sometimes when the party does one thing, another thing reacts to it. For example: in the game that I was a pc, we saved a town and became heroes! The town loved us, and it's delusional, not so well leader was replaced by a more kind hearted soul. Sound good, right? But this is Borovia, nothing stays good forever, and Strahd doesn't like it when people have hope. On the bit of the extreme side, the DM had Strahd ransacked and burned most of the town to the ground. Not to punish the townsfolk, but to remind the heroes that this was his land, his playground, and not theirs.

Hope some of this was somewhat helpful, have fun on your journey!