The 12 is o.k.
Have you seen one in person? They are a smidge small and if you get it you may get the upgrade bug sooner than if you got a 24.
In your area I'm sure you could find a used 24 in good shape but that is up to you.
Things you will need:
A stand. With a 12 you could get a little nightstand somewhere like Target or Ikea, or get the nano stand.
Water source- Will you buy an RODI or get distilled water from the store? (FYI-
www.airwaterice.com has the best RODI units. I bought my Typhoon from them and I LOVE it).
Powerhead (Maxi-jets are nice, they come with stock powerheads but I would upgrade and use the stock one for mixing salt).
Heater (I have an Eco Jabra from Premiumaquatics.com, low wattage, you could wait to buy this until the fall)
Salt, gotta pick. Right now I have Instant Ocean but plan on trying Topic Marin next. Everyone has their own views on which salt is better.
Live Rock- I went with Premium Aquatics Marshall Island Live Rock. It's nice.
Substrate- Crushed Coral or Sand or Bare bottom. I went with sand but again, lots of variations. If you want a little sand sifter don't get crushed coral
Test kit- I bought the master test kit from Dr. Foster and Smith. It's o.k. I have heard good things about another brand but they are costly. I think it's like Seachem or something close.
I think it would be cheaper to get a Nano over buying all the spare parts, plus they just look cool (In my opinion).
Have you looked into the new Oceanic cube that is coming out? If you want PM me and I'll forward you a link about it.
A picture of my setup, this is a 24 gallon Nano Cube:
What kind of fish did you want to keep?
