Hi, guys!
This is my first post here. And i need help

I'd like to receive sugestions to organize my academic ebooks library.
I have some ebooks in ePub e PDF formats. Most of these PDFs are from academic articles. And i also have some of them generated from internet articles. Today i have a folder with some subfolders in my hard drive synked to an external HD (for safety backup) and my Google Drive account. In addition to the computer, i have an Apple iPad and a Android smartphone.
For now, the best option seems to be using Google Drive as a cloud service. But i know this way isn't the best.
I tryed to use
Mantano Reader. But it doesn't have access to my cloud library. I would need to send all my books to iPad and Android Phone. And my collection wouldn't be automaticaly updated. Besides, it has some real interface problems.
iBooks requires to have all my files saved in my iPad. And it wouldn't be available in my Android.
Google Play Books looks to be a better option for now. But i can't create collections. And it would't let me organize files by subject.
So, this is my question: is there any way to organize my files in my computer (synked to a Google Drive, Dropbox, OneDrive or any other cloud service) and access this files in any app on my devices: iPad and Android Phone?
Thanks a lot!
By the way: is there any way to transfer books from Kobo to another app?