1. I would say no. Porcupine puffers from what I know, like to swim and grow to be around 10". The only puffer I would reccomend is the Valentini Puffe. They get to about 4", and I have heard places where they are kept in a ~20G tank and have a ton of personality.
2. *Most* puffers will eat corals, if not all. There are a few expectations. Chekc this out. 17G tank w/ Valentini puffer and corals. http://www.nano-reef.com/forums/inde...owtopic=159225
3. I would never put a Mantis Shrimp in with a puffer. Dependant on the size of each, and the size of the Mantis, one will eaither get killed or seriously injured (Puffer try to eat shrimp, shrimp attack, etc). Also, the spearer Mantis's will attack fish.
4. That should be fine. How deep is the sand bed, inches wise?
5. A general rule of thumb is 1-2lbs per gallon. It all depends on what you like. LR is the main type of filtration, so I guess the more the merrier. Make sure you have space to incorperate swimming space and coral room, however.
6. I would get two powerheads. And, you need the actual tank, proper lighting, rock, sand, heater, and care for the basic setup.
7. Well, what are you going to keep in the tank? Once we determine that, then we can decide. Right now we dont know. Once you decide the fish and/or corals.
8. Substrate is your sand, and its main purpose is to hold biological filtration. It also looks better (IMO) and many creatures benefir from it.
9. I will tell you the safe levels for reef.
'trates: 5ppm or less
Alk: I am not 100% on this, as I have heard everything.
Calcium: I belive it is 450-500. You need to check on that.