get yourself a couple hydor koralia powerheads... they are fairly cheap... as for other equipment we would need to know the size of the tank to give you the best info... are you going to be running a 55g starting out or are you going larger? as for the substrate(seafloor material) go with a Caribsea Aragonite gravel... this is soft enough for burrowing creatures as well as large enough to see, then again Im just not too fond of fine grained substrates. If you are looking for something "finer" grab some fiji pink sand, its got a nice color too it and still has the natural look you should strive for.
Another question is do you plan on keeping coral? If so you will want to look into lighting... If you plan on keeping SPS, Clams, or Anemones then you should get a T5 or MH light setup for your tank size. If you plan on just keeping fish you dont need anything too special just a little bit to keep your coralline algae on your live rock will be enough. Power Compact lighting would be sufficient enough even on a large system to keep the life on your rock thriving.
Just to prevent a disaster make sure you are doing your homework, its quite an expensive hobby to get into so the last thing you need is things dying. Saltwater is not as hard as people make it out to be but it does require a certain amount of husbandry to keep it going steady. Learn about each and every fish you plan to keep. Also make sure you are learning about proper testing of your water parameters.
To answer the very important question about what kind of water to use... This is done many ways, including tap water. Now tap water is surely the worst thing you can use but many people do just fine using tap water. Distilled water is better than tap but still not as good. I would recommend using atleast a carbon filter for your water, dont just dump it in from the faucet. Over the long term bad water can ruin your tank especially if you are living in a urban area where there is chlorines and heavy metals in the water. If you live in a rural area a thing to keep an eye on is the farming industry, they use lots of poisonous things in their fields that will completely "pwn" your sw tank. The best route to go and this is agreed upon by 99.99% of people is RO/DI water... The RO/DI units are spendy but in the long term they will provide you the best possible water available. If you cannot afford the RO/DI unit right off the bat you can purchase RO/DI water to fill your tank and top off as well as water changes. Another route if you live on one of the coasts you can probably find Real Ocean water at one of your local fish stores. It can be spendy but its already got the salt mixed in and you can have the store test the parameters right in front of you.
I hope this information helps... Also I would like to say WELCOME ABOARD! We are glad to see new faces here at the Aquarium Forum, take advantage of all the information you get here, just make sure you pick an opinion try it and if it works stick to it, that old saying "If its not broke, dont fix it." Applys to sw aquariums as well!