You can cycle the tank initially without fish, I've done it many times without any probs.
First of all, from your post I'd guess you have the test kits needed - Ammonia, Nitrite, Nitrate and pH are the key ones. You can buy a kit with all these in (most manufacturers make them) and upon setting up (which you already have) try adding some aquarium water from a friends tank or from a shop (most will oblige) and leave the tank running for 1-2 weeks. Then start testing the water every 2-3 days until your readings are as follows;
Ammonia 0
Nitrite 0,3
Nitrate 0
pH All depends upon area, but for most trops you're looking at between 6.5 and 7.5
If you can't get hold of tankwater then add a very small amount of fishfood (a couple of flakes or so) to the water after 5 days of setting up, ensuring that it sinks.
Once tank has cycled (as cfc said, can take up to 6 weeks, but usually 2 weeks or so) then, as suggested, add 2-3 small (1"), hardy fish and
keep testing the water every 3-4 days or so to ensure filtration is working as it should.
To build up stock; Add 2-3 small (1") fish every two weeks or so until tank is stocked.
Ideal starter fish; As cfc stated, Zebra Danios are ideal, as are your Cherry Barbs. Golden Barbs, Red Eye/Buenos Aries/Black Widow Tetras are also good. Corys introduce last - Ideal first Corys are Bronze, Peppered and Albino (forms of bronze usually). These are toughest.
The key thing to remember - Don't rush things. Take your time and enjoy the experience! Good luck
