Noobie needing tips

[Fort]

How long have you been in the fish keeping hobby? Salt water can be difficult for the new Aquarist. It sounds like you need to goggle and do some reading, especially on what a sump helps with. There is tons of information all over the net on this subject.
Getting a pre owned tank set up is a good idea you can often find full set ups for a lot cheaper then store bought items. Buying a chiller some say might be necessary really it depends on your set up, whether getting natural sun light, does your residence get extremely hot in the summer.
If you purchase cured live rock you can add fish right away but usually best to wait a day or so and test for Ammonia levels. I don't recommend you add coral, coral is for experienced hobbyists only.
As for the dead rock, if you clean off old live rock and add one piece of cured live rock, the organisms on the cured rock should spread and bring life to the dead rock. The same can happen with sand.
Start with fish only system and give it 8 months or so and see how you do before trying a reef tank. It is a very expensive hobby if one fish gets sick and spreads the disease around.
From your list of questions it sounds like you have a lot of reading ahead of you if you truly want to do it right.