Premium I assume? Very HUGE BUMMER that Joy shut down Harbor
THe folks at Premium have always been nice & helpful & I have bought dry goods live rock & livestock from them at very fair to very good prices.
Picking the live rock - that really depends on what your set up is intended to be. If you want a lot of zoo and have shy critters get lacy rock, ledges/slabs & make caves; if fish only & rowdy ones get LARGE hard to move furnishing. If for diggers get PVC as well.
I really really rec that folk NOT buy all their live rock at once if they have never set up a tank b4 and will have the chance to get more. You will find more rocks you want - for shape, because they are just right for that spot, or you find a great mushroom rock or a different coraline color.... Also if you get the rock at different seasons and from dif areas you max your micro livestock. After living with a tank & your livestok you may want to change, add and rearrange for flow or to settle squabbles, yada yada. It is a good idea to add a new rock as you add a critter - this changes the terrortory for the "Ruler/present occupant" and puts new & old on a slightly more even footing. By "New" I mean new to that tank not UnQuarentined.
You should quarentine (I cannot spell that word) Live rock. seriously. Put into a tank that you will use for Q for your other livestock. After 2-4 weeks you should see a lot of itty bitty things, check AFTER DARK with a red covered flashlight as well as periodically whenever you pass. Pick up & shake the rocks and examine them - leave in water while you check them.
Doing the hyper saline dip - if you're getting LR from Fla or carrib at this time of year, maybe but otherwise I would just quarentine in a bare tank. Last time I was at Premium he was carrying South Seas LR, nothing from Fla, keys or Caribe. Is good to have a few live rocks in the Q tank anyway, helps the fish or other stress less. If the critter has a parasite in the Q tank just leave empty of critters for 6 weeks. DO NOT EVER treat live rock with chems or metals or anything really but esp copper. If you Q the live rock for min 4 weeks you can be realitively sure there are no parasites to bug your critters. [sorry couldn't help m'self] 3 months certain. If you do the Hyper saline dip you loose some of the reason you are paying good money for wet rocks.
Can you ever be positive any live rock is safe? No. I've got 3 aq I have not put any new lr in for over a year, just found a mean grumpy fugli crab! In a tank I check multiple times a day (one of my fuges, 20 gal LR & algae & zoo only ever) had Q'd the LR & examined each piece. Many times. He is about the size of a half dollar or 3x4 cm roughly. But I also have the coolest variety of pods & worms & all kinds of things. Even an incredibly teeny tiny banded sea krait. Ok fine, it's probably really just some cool worm esp as I have never seen it swim only crawl vertically. Have an interesting star in another tank that might be 5 cm arm tip to arm tip, maybe a serpent? My requested (& recvd) birthday present this year was as many of "THE Modern Coral Reef Aquarium" volumes as we could afford. Hubby happy cause when I call for him to "come see! really interesting new thing" he asks what it is so I'll go look in one of the books and if I manage to find it he doesn't have to get up & if I don't find it it's gone by then so he still doesn't have to get up.