Power filters work just fine in salt tanks, you just have to remember to keep the filter media clean. One thing I really like about using filters is not only do they remove particles from the water, but you can run carbon in them which will help to keep the water clear.
Skimmers can be vital for reef tanks specializing in sps corals, or even lps corals, but in a fish only tank, well, you might not need it at all. It really depends on whether you will do the necessary water changes without fail that the tank will require. If you have any doubts at all, then by all means, use a skimmer.
Things that show up on LR? Well, that really depends on the type of rock you buy. The more porous the rock, the better (I have a large portion of my rock that has been aquacultured and this rock always has tons of stuff on it) some of the critters......snails (I got some whelks that haven't bothered anything, and some keyhole limpets), a bumblebee snail, seasquirts, sponges, tunicates, small brittlestars, bristleworms, various pods, razor macro algae, featherdusters, a beautiful micro algae that looks like encrusting red velvet (the small pods love to graze on this stuff), button polyps, unknown crab, three large clams (not the colorful kind) and two smaller mussels, some small sps corals that have managed to survive, oh, and a small worm that used to glow neon blue when the lights were off at night, also a couple of large swimming worms that use to come out at night too.......