I have my replacement Kindle now and here's my strategy, focused on loading books, as for me that was the one thing I ran into trouble with right away:made it unstable.
Now I have started from scratch, so I know exactly where I am, if something goes wrong. By loading small batches I try to keep some control over the process.
I load about 50/150 books in one go---leave it to charge--check once in a while if the indexing has finished (with random search xhfbdsk etc. gives the number still to be indexed)--if I see one book is indexing more than half an hour (a 'normal' book); I deleted it via Calibre--once I've checked indexing is done, I start the next batch....and so on.
I think it's best not to do anything on the Kindle while indexing a load of books, and only load other ones when you're sure the indexing has been done.
Also look sharp at the upper left top of the Kindle, the spinning wheel; it also gives an indication wether the Kindle is still working on something. You don't want to do several things while that's spinning.
I know it's rather troublesome, but my Kindle seems to be good now. I've loaded appr. 500 books .
Good luck.
And phone twice with Amazon if you think you can get better/faster replacement. It worked for me from 9 weeks to 3 days (overseas!). Really; I was amazed, surprised and glad at that speed of delivery.