Have read through everyone's posts, and just want to add a bit to it.
The use of your "tap" water is subjective. If you live in boston as a for instance(just saw some data on their water, cleanest in the entire country) and your tds is at near 30, and you don't use chlorine, and there's no "junk" in the water, sure. Use some water treatment stuff and your FINE. However, if your tds are 499, the chlorine is through the roof, etc. it would NOT be a good idea to use it. If he is very local(within 1-2 towns from you) he should know the water quality there, and it IS possible for you to use it. If you are further, he may not know what your water is like. If I did not know everything in the tap water, I would not personally use it.
In a 30-gallon, I have to agree, if you want sps or lps corals, you cannot use the "stock" PC lights. I have seen/heard of t5 retro-kits, while that will jump your price up a bit. I'd say 4-t5's.
The LFS, the guys sounds good. He is admitting that he understands the online issue, and seems like a good guy. You can feel free to support him and his store, he is not telling you complete lies, at least that I can see. If you are buying LR from him, and it is cured, you will have little to NO cycle. This can be a little problematic. If he has it, it is only enduring the very short ride in your car home, and very little will die. To some point you need this dieing/cycling. It is what forms the bacteria that will continue to breakdown all ingredients in the cycle. Ammonia, nitrite, nitrate. You can easily do without much of a cycle, but if you do, your tank won't be AS ready for livestock. When you would add one fish, you would have a mini-cycle. Your tank regularly goes through cycles, it is just that most go un-detected, and for good reason. A mature tank(6 months+) won't even barely show an ammonia spike AT ALL. But every time there is an added bioload(fish poop, food, etc.) there is a cycle. The larger the initial cycle, the less following cycles will be when you add fish. Kinda confusing, I know, but after a little while you will get the hang of it. I have heard a few people speed the cycle a BIT with some fish food. If you have some flake food laying around, throw in 2-3 flakes every day. This will give you a bit more bacteria to work with, and lessen later cycles.
IMO about the RO/DI. Get one, you won't be sorry. Also, I don't think you need something in the 75-gallon range if you are willing to wait. As I have heard the worst thing you can do is rush, I took this advice, and worked out fine for me so well.
I got a 24gpd 3-part system(I think about $100) and Added the DI (for another $49). I just did about a 7-gallon WC to keep my ammonias a little lower during the cycle, and started with about 16 gallons in my 20-gallon brute trash can. Had about 9 gallons left, knowing ROUGHLY 1-GPH, sleep for 8 hours, I had plenty of space for it to run all night. Turned my faucet on, went to sleep, woke up and have about 18 gallons in my drum. That is efficient to me. If I had a 50, I could not go to sleep with it running for only a 20 gallon can. With a 30, I'd suggest more than 24gpd, but a 50 is JUST FINE IMO. Just have a container that holds enough water for about a 90% change at any time when it is needed. By doing this, should there be an emergency, you know you have a FULL water change ready. Just my $.02.
The store owner told you nothing out of line IMO. He said the main cycle..(ie. ammonia spike) would take 7-10 days..probably pretty accurate..would I add a fish at that time no but he wasn't way out of line especially if his live rock is cured. Secondly, RODI units alright he was a little off on the production..not a biggy for me. Thirdly, you really can't expect a person to give you all the answers you want or have preformulated..it just can't be in an opinion based hobby. Fourth, tap water use would depend on the TDS in your area..if it is very low it wouldn't be the end of the world to use it initially..many people use it always. IMO he was trying to save you a bit of time/money and all in all gave you decent advice..
