Well wouldn't the KOBO readers do that? They support epub, and have Android and Windows apps.
The catch is they only sync highlights/notes for Kobo store books.
If you want true cross-platform syncing of any books you own from any source, best option I'm aware of without paying for some kind of fancy web hosting service that handles that for you, is to go with Amazon which means you'll have to give up on the epub format idea. Trust me, been down that road, similar thought process, gone full circle and now I'm back to Amazon. But it actually works pretty nicely. You can change the extension of .epub books you get from non-Amazon sources to .png as summarized
here, then send to their email conversion service, and they'll convert the epub to a format you can put into the Kindle devices and apps. Then they'll sync your highlights/notes across all the platforms.
ETA: One other thing I just recalled, don't know if this is an option for you. There are a handful of web services that will actually host ebooks and your metadata for them (notes, highlights). You use their app ecosystem on Android, Ipad, or desktop systems via web browser, add your metadata, host your data on their web services, and they sync the notes across all your devices for a monthly charge. One such is
Bookari, which has apps I know in the Google Play store, and the premium version of their book-and-note hosting service runs around $50 a year. I considered this before, tried it briefly, and found at the time Bookari was very sluggish and unreliable. It may have improved since then. Also, while they support all mobile devices and desktop platforms, I'm not aware they have any e-ink device support. Also, there are a few other services of this type out there, others here may have ideas. In general, for myself, it didn't make sense to continue my quest to find an epub solution I'd have to pay for, when Amazon's store has the best ebook selection anyway, and gives you this highlight-syncing feature set for free. All I had to do was give up my quest for an epub format solution, after that it was easy. :-)
A free version of such a web service is provided by the app FB Reader. I've used that on and off for some years, but never very satisfied with it, and finally gave up on it. They have Android and Ipad apps, but to my knowledge they don't have Windows or web browser based reader apps, and of course no e-ink reading devices either. They provide 'free' notes hosting for your books when you capture the notes in THEIR app, and provided that you supply your own instance of Google Drive (they don't support other cloud storage providers, last I checked). This is actually an epub-based solution, as FB Reader supports epub. But as I said, it's still not what you want since it doesn't support desktop OS's or web browsers or e-ink devices, so you're limited to mobile devices.
So back to the beginning: the best solution I can suggest--keeps your cost down, and meets all your requirements EXCEPT the epub file format--is sticking with Amazon Kindle.