You'd want to split between base rock and live rock--the live rock will come with hitchhikers and cool things, the base rock will become live as things spread. You could go with all live rock, using some base rock is just cheaper. I'd start with about 5 pounds of base, add at least another 5 of live, and maybe boost that to 8 of live.
Testing salinity is done with a hydrometer (actually, you're testing specific gravity, you want to shoot for about 1.024-1.025). Little plastic jobby with a swing arm will work fine, though you may want to calibrate it off a spectrometer (LFS should be able to do this for you) for accuracy. Hydrometers tend to be off, but reliably so (example, it tests 1.023, but the water is actually 1.025--so you know it's always reading .002 low).
The powerhead will probably be needed to provide current in more than one location and reduce dead spots.