Generally you will want at min 1lb of LR per gal, however, this is not necessarily what you have to do. You can use a lot of base rock and seed your aquarium with the live rock of your choice. Eventually your base rock will be seeded with the coraline from the LR---at considerably less cost. Fiji is good rock because it is lightweight and porous.
You should be sure that no rock is leaning against your aquarium. Building your rock up against the glass of your aquarium can result in disaster as all the weight will be on the backside of your tank leaning against your glass, which could stress out the aquarium structure. Also, you want good water circulation throughout your rock structure, so you will want passage ways and open spaces throughout so that good water circulation can take place.
Picking out your own LR has its advantages because you get to eyeball your pieces; however LR at LFS is usually more costly. This site sells some very good quality LR—according to members who have purchased from here.
One way you can minimize the possibility of acquiring unwanted creatures is to leave the LR out of water for a few hrs once you get it home. Basically, you can put down a tarp or trash bags, lay your rock down setup salt water in a dedicated spray bottle, constantly spraying the LR while you wait it out. This process will usually draw out any unwanted creatures. Additionally, while you doing this, you should also clean up the LR a bit, removing sponges, etc, that will die off anyway.
Hope this helps.
