Just finished the last volume of the series.
“So was it worth it?” you might ask.
I suggest reading the first three books.
Wait a long time, like a year, and then read 4 and 5 if you want. Books 4 and 5 are sufficiently similar to 2 and 3 that the amount of redundancy and repetition will become tedious if you read all five in a row.
Either way, don’t bother with 6, the one I just finished. It’s not terrible, but it’s not necessary either. The end of book 5, Shelters of Stone, is probably the most satisfying conclusion of any of them.