If you are looking at getting a jawfish for that size of tank, I would build him an enclosure out of PVC pipe. It is essentially a small square with a small piece of pipe coming out of one side that comes out of the sand. Here is a link to the forum on how to make it.
http://www.nano-reef.com/forums/inde...053&hl=jawfish
Otherwise, you are going to have to have 3-4 inches of sand for a minimum.
As for test kits, there are 2 really good ones. I use the Salifert brand, but I know a lot of people use Elos as well.