Upgrading Library

Welcome! [:)]

I recently added over a thousand new resources to my library, but the iOS app is taking forever to download them.  Is this normal?

Well, I guess that depends upon your internet connection. 

Will it download the resources in the background, or do I need to keep the app open at all times to download them?

No. You need to baby it.

I should point out, however, that it is NOT recommended to download so many books. Unless you live without internet for weeks/months at a time, I would suggest being much more judicious. 

Is there a way, on the iOS app, to choose which ones to download and which to not download?

Sure. 

First, you can see what is downloaded by going to the library and using the syntax local: . Downloaded resources should have the "circle i" icon filled in blue. If you press on the icon, the book's info panel opens up, including a "remove" button. Pressing that button with remove the download, but the resource will remain in your library. 

Second, you can remove the filter syntax used above and press on the same icon to download resources of your choice.

Third, and perhaps a better solution for maintenance purposes... You can create a tag in the desktop app (L6) and apply it to resources you want downloaded... or perhaps you have already tagged the books you want. For example: Maybe books you own on "family" are what you want to download. In the mobile app, type: mytag:family where "family" is the tag you gave to your books. Any books you tagged with "family" (and which are mobile enabled) should appear. Clicking on "download all" while the library is filtered will download ALL the books that meet that criteria and nothing else. 

If I've downloaded ones that would be best kept off, can I start over?

I shared with you how to remove books, but you will need to decide which ones to download. I typically keep a small collection of reference works, study bibles, etc. along with books I am currently reading or part of a reading plan.