[BookCat]

Start using Calibre. Put all your books into there. If you want to, add some tabs, or maybe even add some blurb, to your books.

I always think - and I'm in a minority - that it's best to add a few books at a time, maybe ten or so. Create some Collections on your new Clara and add books to them as you go. (For me, this is half the fun of putting 'new' books on my reader.)
Transfer the ones you want to read soonest first. Then when the battery needs topping plug your ereader into your computer and add a few more while it charges.

This is more or less how I do it.