Starting SW couple questions?

Wowsers! Sorry for the late reply!

Congratulations, that was the first tank I decided to go with myself. About a million years ago, that be...

The small systems are pretty easy, though water chemistry always gave me some problems. That said the pump it comes with should be sufficient. In the nano systems, the space taken up by the smallest powerheads versus the flow they produce is usually a zero sum game. Flow will always be a bit of a problem, but without a bigger system I wouldn't mess worry on adding more.

I haven't dealt with live rock (LR) from wither of these sources, but either should be fine. Smaller pieces will give you more freedom to decorate, but larger pieces mean less work in a nano system.

Live rock comes in a variety of sizes and shapes. In my tanks, the heaviest are situated out in the sandbed with the smaller pieces resting on top. That way the base is the strongest. I've seen people use coral putty to affix the pieces together when the risk of a large of rock moving fish necessitated it but I really don't see any need to. So long as your rock sits in place, and won't tip with gentle force, you should be fine.

Live sand is a bit of a contentious thing right now. The sand bed provides a breeding ground for filtering bacteria/organisms that will help keep your water in good shape. The finer the grain, the more room for bacteria to grow. The deeper the sand bed(DSB), the more room for bacteria to grow. The problem is, you need to get that sand bed to 5 or more inches before you'll see that benefit. I ran an inch or two in all of my systems, but that was for burrowing rather than filtering. I.e., gobies, blennies, sand-sifting stars, nassarius snails, etc... You can throw some in but in a system that small it will be for aesthetics.

In my experience, be prepared for frequent water changes and some frustration. Nano's are great and exemplify the best and worst of the hobby. Keeping so few things in it will help immensely.

Good luck!