Good luck finding a smithii. I already went down that route and after a few weeks of waiting, I settled for a N. Wennerae. The LFS hasn't caught on that Mantis shrimps are in demand...many of them don't even take the time to ID them. You can get a sure thing N. Wenn from TBS.com..but you will have to look hard for a smithii.
Pete has been great though..he's always active building and exploring the tank every day and night. I couldn't ask for anything more.
I've got a 6 gallon cube tank that I made out of 1/4" glass. Behind it is a 2 gallon sump that holds the heater and powerhead, and eventually a nano skimmer (it's apparently in the mail...). There's a 2" deep fine aragonite sandbed, though in hindsight I wish I'd put in a coarser grade of aragonite. I had about 10 lb. of rock, but I'm down to just one 5 lb. rock in the middle now; the tank was too cluttered. I actually just pulled out most of the rock today. The rock is covered with aipstasia, and I have chaeto along the back wall. Two Coralife 20W 50/50 bulbs light this sucker up pretty good. I plan to add more rubble to the tank so my mantis can use it to build a little cave.
The salinity seems pretty stable. I top up the tank with distilled water a couple times a week. I'm sure the temperature fluctuates a bit. I pulled out the floating thermometer a couple weeks ago, and a digital thermometer is in the mail (with the skimmer).
I found that with most of my tanks, the temperature usually stays pretty stable in the winter when the room temperature is less than the tank temperature. In the summer, unless the A/C is on, my tanks tend to heat up quite a bit. I can't really do much about that, so I stopped worrying about it a couple summers ago.