I have a 1.6ft fish tank, I want to set up a tropical community tank,...

Cycle the tank BEFORE you put the fish in it. Here's an article on how to: http://www.aquatic-hobbyist.com/profiles/misc/fishlesscycling.html

Set the heater at which ever temperature your fish require (most tropical fish do well at 24-27 degrees Celsius)

For fish, Betta's (Siamese fighters) do well in small tanks and maybe some corydoras or if you don't get a Betta then you could get guppies.