New to SW and have some questions

So I got a 12 gallon JBJ Nano Cube DX used on trade yesterday. It came with two fish, some snails, some hermit crabs, and an anemone. The folks who sold it to me put all the live rock and sand in a bucket with tank water for me to keep it happy. I then put all the fish and snails in another bucket. All of the livestock minus one sneaky snail went to the LFS where I got store credit.

I took the tank home and set it up. I put the sponge filters in the first chamber, then carbon in the second, and biomax in the third. It originally had bio-balls in the third but I tossed those out in favor of the ceramic media.

One all the sand settled and I could see in the tank I set up the live rock how I liked it. I'm wanting a little more rock for decor purposes but also filtration purposes. It's got around 10 lbs of live rock, or so I'm told.

I got new pre-mixed water from the LFS and replaced all the oringal water with new.

The tank also came with an API saltwater test kit, a hydrometer, and a few other little things.

Since setting it up I realized it had some shortcomings also. I purchased a heater for the tank (don't know how they got by without), a small powerhead (the current setup is 100 gph and the new powerhead adds 240 gph), I ordered an API reef test kit, and some calcium supplements to help my corraline come back. I also ordered a book on SW tank keeping because I'm a student of things I'm interested in.

So onto the questions...

1. I realize that water evaporates over time but salt doesn't so the salinity will slowly increase. I can add RO/DI water if I can find it or distilled if I can't. Do I just make a note of the current water level and then keep topping off until it reaches that level? What happens if I add too much fresh water and if I do how do I resolve it?

2. Is it worth mixing my own saltwater or not for a tank this size? I can't recall what my LFS charges for water but I feel like a 5 gallon bucket was less than $10.

3. The plan for the tank is only one or two small fish, a few corals, and a few snails. How often do you suggest I do water changes once that happens?

4. The second powerhead I'll be putting in, where to put it? Opposite the first, same as the first? Do I put it on a timer to only run sometimes or run 24 hours a day?

5. What do you think of the filtration setup I mentioned? Do I need the carbon or should I replace it with more bio media? Should I add a protien skimmer and move the foam to the second position?

6. Do I need to keep the lights on during the cycle? Is it beneficial to keep the coraline healthy?

7. I'm not buying any fish or coral until I know the tank is cycled and ready, but what suggestions do you have for coral for this 12 gallon tank? It's got two 24 watt CF bulbs, one white one blue. Keep in mind I'm also new to SW. I've got a few ideas for fish myself.

I know I'll have more later but that'll do for now. I'm hoping my cycle goes quicker since the tank and rock had already been setup for a few months and only had to be moved a short distance. Thanks for all your help.

 

See my answers in red

Yes, this is how top ofs work in the basic level. You could also look into an ATO setup to do this automatically. On a smaller tank, your salinity will be affected by evaporation much quicker. On my 30 gallon I was topping off daily until I switched to an ATO. Try not to add too much freshwater. When I did, I would do a waterchange. This would replace lower salinity water with normal salinity water. I'd repeat until salinity was right over a few days.

I always prefered to mix my own saltwater. I'd know that it was fresh and exactly how I want it. Cost wasn't the primary reason for me.

I'd keep small water changes weekly or bi-weekly. Personally, I was much better doing water changes when I kept it on a more frequent schedule. A tank this size will be hard to keep parameters stable (less water = less margin for error). So frequent water changes are ideal

This one is up to you. I'd put it someplace that would make a lot of chaotic flow. I run mine on a controller for a wavemaker... but it probably won't make a huge difference, especially at first in a beginner tank. I know running 24/7 was how mine started.

I'd keep the carbon, and would personally run a Protien Skimmer.

No, you don't need the lights just for the cycle, though it doesn't hurt anything. It would probably help your coraline too to have em on.

I'll let you do your own research on fish, since I haven't looked for anything in that small of a tank (probably a small goby or something would work best?). For starting coral (and idk enough about CF bulbs, so I can't tell you for sure how they'd work light wise), I'd stick with Xenia (if you're ready to prune it!), zoas, mushrooms and rhicordia. I also think Sympodium look great, and I've found them very easy to care for.


I'd also highly suggest a refractometer over the hydrometer

 

Just keep researching and asking questions.