If your primary idea is to mainly just have your PCs investigate a village and then deal with Strahd von Zarovich himself... I suspect that perhaps Curse of Strahd might not be the right adventure for you to use for this, but rather the original I6 Ravenloft module.
If you don't want to buy in to the idea that there's this valley of desperate people in villages all under the thumb of an overlord, all of whom are trapped here and unable to escape... then all the extra adventure sites in CoS don't really help you. Whereas the original I6 modules only has the Village of Barovia and the Castle Ravenloft itself-- the two locations that your original query seemed to indicate you wanted to deal with. So that module might give you what you want better than the full CoS book would. Plus it's a lot cheaper... $4.99 on DMs Guild as a PDF download, rather than the $30 for the full book.
In answer to your other questions....
1) Whether or not Strahd is known to be a vampire depends entirely on what you choose to make the backstory of the region be, and how many villagers have been in Barovia and for how long. The various Ravenloft adventures (I6, Expedition to Castle Ravenloft, the Ravenloft campaign setting, Curse of Strahd) have seen Strahd in power for so long that it's assumed that many of the people know he's not human. Expedition does try and insert a misdirect that says that Strahd portrays himself as the 7th of his line or something, but that asks the players and the PCs/NPCs to believe that there's been seven generations of the Lord of this Castle having a lone son, and that son being named Strahd too, and who just happens to look very much like his father, and grandfather, and great-grandfather etc. But I think most people just write that attempted plot point as a bit contrived. So with a guy who has lived in this Castle in the mountain for more than 400 years... yes, people probably probably assume he is undead, if not know as a vampire directly.
But again... if you decide to change the backstory of Strahd to every having happened with his brother and Tatyana within like the last 10-25 years (and Ireena is a reincarnated Tatyana that occured almost immediately), you could certainly not make it as obvious that he's a vampire because there hasn't been the time for that story to propagrate.
2) I haven't run it with higher level PCs, and indeed downleveled it for PCs starting at Level 0. But the beauty of 5E is that you can just insert an additional monster or two or three into the various encounters and reach applicable challenge levels for the party. As the Castle itself is meant for Level 8-10 PCs, if your players are even higher than that... just having more random encounters inside the Castle that involve higher-level undead more frequently (spectres, wraiths, phantom warriors, etc.) you should be fine.
3) I also have not use PCs with lycanthropy and don't think I would, mainly because of the fact that lycanthropes aren't like druids with Wildshape-- when they transform, all their clothes and equipment fall off and don't change with them. For NPCs and monsters, that's fine-- they leave their stuff wherever they transform and go back for it later. But for the PCs that would be a major PITA-- dropping everything they have when they transform, transforming back wherever they end up and being completely naked and without equipment, and then having to go back to wherever it was they transformed in the first place. I don't foresee many of your players wanting to deal with the hassle of that... especially considering their characters will probably be more powerful in their adventurer forms with their armor and weapons then whatever the lycan form is.
If you wanted to have a PC get bitten and acquire the disease as a problem to overcome, then sure lycanthropy would work great for that. But as an ability that the entire party has? I don't see them really wanting to deal with it or use it that often.
