Strahd is trickier to run than any other Boss out there because he shouldn't be run like any other Boss out there.
1) He's bored. His universe is mostly shades and shadows. He doesn't have new things to entertain him, and that's part of his curse. There were several Ravenloft novels put out back in the day ("I, Strahd" is his personal story that has tons of source material to flesh him out), and for Strahd powerful beings new to his realm are playthings. He doesn't destroy his toys. Killing the PCs is the easy part. Breaking their morality is a task. Surviving Strahd can be a roleplay balance of keeping him interested in you (if he breaks you too quickly, he gets bored).
2) He's eternal. That can't be stressed enough. He can't die. Even if you destroy him he can't die. He'll just come back. The Dark Powers that created this prison from his darkness love the suffering. Fighting is boring to him. Corrupting another into hopelessness, the game is on. One of the worst parts of the module was the suggestion Strahd randomly shows up in the country and attacks ("haha, I'm a godlike being and you're 3rd level nobodies, haha, eat fireballs, haha"). Whoever wrote that bit hadn't read any of the novels. But if he ever gets to the point he has to "lower" himself to a physical resolution, and he's not the one who would ever start it, he'll finish it.
3) He's a wifebeater, sorta. It's a character flaw, his obsession with making Ireena / Tatyana love him through coercion and his dark powers. He wants to isolate them, make them see how awesome he is and how lame others around them are. Having a character flaw should play a part in defeating him, not simply be backstory fluff. Same with his diary. You've got a chance to give a treasure trove of insight and see what PCs can do with it. But, it makes what he's doing more exciting than combat. He's playing psychological games designed to break Ireena down, make Ireena feel like the reason everything bad is happening is because of her "choices," until the only choice is to go to him.
4) The unwinnable battle. This is the epitome of what distinguishes this Boss from any other. Every other Boss stands up, you dish out some HP damage, there's a phase 2 where the Boss gets some second wind or help, and the PCs dish out some more HP damage. His design, however, can frustrate players who expect every encounter to be balanced and winnable, because they have been conditioned this way through game design. Monsters are supposed to stand toe-to-toe and slug it out. Strahd plays to win and that means not playing "fair" for players. Beating him should be a major accomplishment, achieved through understanding how to overcome his invincibility.
That said, you indicated your players are "new." If they are used to the formula of: monsters spotted --> roll initiative --> kill monsters, this can be an opportunity to chat about how Barovia isn't that place. There's going to be monsters who don't play by the rules, who might be way over your power level, and you'll probably die in a straight up fight. Or in the late Gygax's words about one of his dungeons, this is a "thinking (wo)man's dungeon." But don't make it too easy. After all, many have entered Strahd's realm. No one has ever killed him...
While all probably true, almost none of that is what @Retreater is looking for with this encounter. This is not the Strahd you know, but the Strahd he needs. And story and character development and subverting expectations is not on the menu
I think the biggest thing is to just be willing to go against your DM instincts here. It seems like you've already determined there are only two options on the table-- Strahd stays and fights and gets slaughtered by the party in like a round or two-- or Strahd spends hours doing hit and run attacks on the group until they run out of supplies / abilities and they all eventually die.
You might just have to force yourself to select a middle ground that prioritizes the players' fun moreso that following "the rules" or "realistic BBEG logic". I know many DMs hate hate hate to do that... but a person has to really decide what is more important-- a memorable and fun climax for the players, or their own comfort and preference?
It is still possible to do a few rooms of a 'hit and run' scenario without defaulting to "Doing it each and every round for the next six hours until all the PCs are dead". You can have him hit and run with wall walking even just by keeping Strahd on the Rooms of Weeping level-- to give the impression of a big climactic fight, while also keeping the vampire within somewhat of a reach to let the players get hits on him. Make the players chase him across the level. Leave the study and go into the bedroom behind it. Have Strahd lead them out onto the parapets of the castle through the door in the bedroom. Try and toss a PC off the parapets 90' to the ground below and see if they can rescue themselves.
Take the middle ground where you know Strahd will eventually be defeated in the end, but don't just put him front and center to get wailed on with no defense. Prioritize the "story" of the fight, rather than the "mechanics" or the "logic". Just this once.
We had our final session with Curse of Strahd last night, including the show-down with the titular vampire. All told, the fight lasted about 2.5 hours, and the players considered it "epic."
1) Strahd used his phasing through walls ability, keeping the battle through a suite of rooms. This allowed him to recover and perform hit-and-run attacks.
2) The cleric with the holy symbol of Ravenkind - I actually put her in a pocket dimension to battle her possessing demon (which was a part of her background the player had forgotten about.) Once she defeated her own darkness, she was able to join the fight and start bringing the radiant hurt on Strahd - but the party had to "hold their own" until she re-joined.
3) The dwarven paladin with the sunsword never landed a hit on Strahd. He was too mobile for the slow dwarf to reach. But he did battle the animated armor and tried to keep the party on their feet in the absence of the cleric.
4) No one died - but many in the party either dropped unconscious during the battle (or were at least reduced to single digit HP).
Overall, the players were all pleased. We did decide to retire the campaign on a high note to continue with other systems.
Thanks to everyone for their advice.