[terameep]

i'm looking to get one or more ereader apps for the ipad air 2 and iphone 6, both running on ios 11. i'm pretty satisfied with kybook 2 so far, however it doesn't seem this app or it's upcoming sequel won't be getting updates for a long while. so it seems like it's a good opportunity to explore other ereader options.

requirements
the ereader app(s) will need to fulfill the following:
- support file formats: pdf, djvu, epub, mobi, azw3 (can be reduced to support for pdf / epub if someone can clarify the pros / cons of converting mobi / azw3 to epub and pros / cons of converting djvu to pdf, as well as how to do it optimally).
- similar or better page navigation as kybook2.
- similar or better text search functionality as kybook2.
- similar or better support for table of contents / pdf bookmarks as kybook2.
- similar or better text highlighting / notes / markup as kybook2.
- similar or better page viewing functionality as kybook2.
- convenient method to download ebooks from calibre (opds support is best, direct download / file link from browser app from calibre content server webpages is good, compatibility with calibre companion or download from a cloud drive like dropbox, onedrive, or google drive is minimum).

additional considerations
- nice haves would be to fulfill other useful features of kybook2, and to come with their own useful features.
- it'd be really nice for there to be one app that can fulfill all of this.
- two page view is also a good feature i liked from kybook2.
- integration with something like evernote, onenote, or something like that would also be great.
- i don't mind having to figure out how to use the ereader app provided it doesn't take long to get down basic usage, while other advanced useful features are well documented or findable with google search.
- i also don't mind doing some prep work on ebooks, such as adding ebook metadata to calibre, embedding added metadata to ebooks, or converting mobi / azw3 to epub, or djvu to pdf (but not pdf <-> epub, because the converted files will not be good quality, unless my idea of the conversion is wrong).

usage
i mainly read technical pdf / djvu textbooks on physics, math, and engineering for school, most are scanned old editions. it's important for me to be able to view the figures, tables, and diagrams on them well. it's almost as important for me to be able to search the text of the book, even if the ebook doesn't have ocr data embedded, but can be ocr'd and searched. some textbooks or novels will be in epub / mobi / azw3 format.

ebook app impressions
from some research in this forum and apple app store reviews, here's my impressions on the following ebook apps:

- calibre companion: should be the best library management solution, but risky to pay for it considering the app store reviews.

- kybook2: best all in one ereader app to stick with for now, considering it fulfills everything i need at the moment. might consider moving if there are better options that are being maintained. also supports all required formats without any conversion.

- mapleread se: next best thing after kybook2, since it requires file conversions for compatibility with my ebooks and it's currently maintained (at least i think it is)

- marvin: best for epub ebooks

- goodreader: best for pdf ebooks, which is what most of my ebooks are.

- foxit pdf: free alternative to goodreader for pdf ebooks

considered options
the following are the possible options i've considered so far:

1: stick with kybook2. all ebooks readable in a library in one app. ebooks downloadable from home calibre content server with opds. (cheapest)
2: buy mapleread se and use it as the sole app, convert djvu -> pdf, mobi / azw3 -> epub. use similarly as kybook2. (second cheapest)
3: marvin for epub, goodreader for pdf, calibre companion for storage / library management, convert djvu -> pdf, mobi / azw3 -> epub. (most expensive)
4: 3, but no calibre companion. ebooks are instead downloaded via opds, direct download in ereader app, browser app file linking, or download from cloud drive app. (cheaper than 3, but more work since epub ebooks will be in marvin library, and pdf ebooks will be in goodreader library.)

unrelated bonus question: recommendations for ereader apps on windows pc? (app recommendations on this forum seemed to be several years old)

thanks!