Welcome. I have a 90 gallon and it is a perfect size to start with.
For your 90 you will need at least 60 lbs of sand. You can buy live sand but save your money and just buy dry aragonite and rinse it well.
Buy your rock. You will need between 1-2 pounds per gallon. Put some cheap base rock directly on the bottom glass as a good anchor and to prevent landslides from bottom dwellers that sift sand.
Add your sand over the base rock then start your aquascaping with the nicer peices.
There is no fast way to cycle your tank. It takes patience. Start slow and you will be rewarded. The live rock will seed your sand. You can add a raw shrimp to start the nitrogen cycle. It may take a few weeks. Read here as much as you can. There is good information on the new hobbiest thread.