yea, its always nice to get some good experience with
FOWLR before you dive into the reef.
LS and
LR are used as surfaces for good bacteria to grow, and this helps turn fish waste into products which are not so harmful. usually people get a lb of each for every gallon of aquarium.
besides this,
LR is pretty, comes with all sorts of fun little critters like feather dusters and such, and creates a bunch of nice hideyholes for your fish.
as for both, i would suggest ordering online. ive gotten the nicest rock doing that. check out tampabaysaltwater.com or liverocks.com, both are really great places.
as for the sump, there are better people to ask than me. but to make a long story short it is a resivior of water underneath the tank that is plumbed into the main tank, to create room for heater, filter, protein skimmer etc instead of having them in the main tank. it also increases tank volume, which helps you to be able to keep more fish.
in the 150 you could probably have the tang, a royal gramma instead of the pseudochomis, a couple chromis, the perc, and maybe another fish or two.