A couple questions about the Kindle Paperwhite

I have a KWP (6th generation). I used it very often. Here are my questions:

1. Is there a way to add books to collections quickly? I put all the book in a sub-folder under Kindle document folder. But I still have to manually add each book. This is very annoying especially when I have more than 50 books on the device.

2. For word wise function, some people posted here said Kindle creates a .kll folder. I tested this function, it seems that you have to connect to internet to get the file downloaded before you use this function. I would like to know if now I download all the files, then copy it to PC. If I decide to re-read the book and I already delete it from the device, can I copy everything stored on PC back to Kindle instead of using internet download them again?

TIA!