How much rock really depends on what type of filtration you are going with. I would personally go with about 125-140 lbs of live rock and run a sump/refugium to aid in filtration. You can use RO
water and them mix your salt and make sure your water levels are right and then stick the LR
in right after to start the cycle. You may also want to use the cocktail shrimp method to jump start the cycle. You can do some searching on this (often called the "fishless cycle") method here - it is mentioned many times.
Also - RO
water is available from your LFS
for around .50 - .80 a gallon. Many here would advise using just normal tap water because it can cause problems in the future with algae and other incorrect water readings. Some people have nice tap water and swear by using theirs instead of RO
water - but unless you get yours tested and dont want the chance of trouble in the future, I would go RO
. You can also save yourself some time and money in the long run and purchase an RO
filter system to convert your normal tap water to a usable level.
Hope this helps.