It is doable, and you could put some Zoanthids and mushrooms in a 2. with some PC lighting, but I would suggest you upgrade to a 5.5 or 10 gallon tank. I went from a 5.5g to a 15g and its such a nice tank!
there's a butt load of 2.5, 3, and even 1 gallon reefs online... care sheets, shedules and everything..... if you design the lid right you can get the evap to run back into the tank and still have great air circ......