1st of all, welcome sikiee to SRC.
1 ft is very small and bad for newbie. but since you already bought it, lets try to make the most out of it.
Sand bed. Maybe invest a little more and get live sand. Iwarna and Aquamarin sell them.
you would just need prob half a pack to fill up to 1 inch, maybe buy/ share from some of the reefers here?
you can use distill water with salt mix. but you can also buy a bag of saltwater from LFS.
If you are cycling your tank, it is optional if you would like to do water changes.
Some people find it unneccessary since you are trying to get the full nitrogen cycle established in your tank.
Yes you can top off the evaporated water.
I strongly suggest you start off with a fish only tank 1st. Maybe just some small fishes/ shrimps while picking more to get over the learning curve.
btw, a small tang is not considered a small fish. Tangs are under the large fishes categories so dun go by physical size.
your live rocks will have some form of organisms. if you can keep them thriving, cut out the algae, boom some coraline, then maybe you are ready for corals then.
just my thoughts.
enjoy!