Always check the SRP Library.
Hone Lapping 101 - Straight Razor Place Library

Another alternative to the DMT 325 is the Atoma 1200 diamond plate. Use the sandpaper for heavy lifting e.g. first flattening then move to the Atoma. The 1200 will be plenty for everyday lapping on everything 4k & up & will be closer to the flatness of a DGLP Shapton plate than some of the DMT's I've used.