okay let me try to answer as much as i can.
first off, WOW 15 and a 60G tank!? i'm jealous! i have a job and i couldn't afford that!
was good in giving you some stuff to seed/start a cycle, and thats good you know what a cycle is.
a sump is a tank (usually under/in the stand)) that is essentially a really good filter and most house their protein skimmers in there, a refugium allows you to have other critter (copepods, snails, other small things) in the sump/fuge area (like a seperate chamber) you don't necessarily need one, for a 15y/o it may be too expensive except for a basic wet/dry trickle.
for simply a FOWLR
tank whatever light floats your boat will work, it could be a blacklight for all you care, a T5 fixture could support corals if you wanted, so the lights are all up to you.
you'll need an ammonia, and nitrIte test kit for your cycle.
depending on the dimensions of your top you could find a glass top, or even eggcrate to keep fish from jumping.
yeah you can, but if you get lazy with maintenance it would give you a buffer, so i'd suggest investing in one, even if its a hang-on-back skimmer.
yeah if i were you i'd add it all at once, or add some LR
then add some base(dry/dead) rock because if the rock you get isnt cured, you could start another cycle which wouldnt be good for any life you have in there.
starter fish, hmm. of course clowns are nice and easy, i wouldnt recommend any more than a pair and don't mix species of clowns.
this site here: Saltwater Fish: Marine Aquarium Fish for Saltwater Aquariums
has a ton of fish to look at, as well as there care requirements and the parameters they live in, be sure to look at the minimum tank size and the max length, over stocking your tank wouldn't be good.
you are ready to add fish when your cycle is done, a good way to tell is if you have a spike in ammonia, then a spike in nitrIte, then those die down to 0 and you have ~20 or less ppm
of nitrAtes. the gunk you got from your LFS
should help speed that up.
the powerhead sounds fine, koralia makes good ones when you get another.
you can add uncured first, but after that like i said add dry rock and it'll become live eventually.
remember, nothing good in saltwater aquaria happens fast, so go slow and be VERY patient. it's a great hobby and soon you'll want an even bigger tank!
have fun and ask anywhere on here for further questions!