My answers are posted in Red font.
yes, there are fish in the tank (though, now i kind of wish i had a better understanding of all this before i started, i would have done a fishless cycle)... the tank gets some decent daylight on 1 side. I also have 2 plants in the tank.
How many fish and what kind are they? Does the tank get enough sunlight to heat the water up? What is your water temperature now?
do i need to be concerned about the fish as long as the ammonia, nitrite, and nitrate levels stay low and the ph stays around 7? Ammonia can be fatal to your fish and the only safe level is Zero. Nitrite level should also be Zero. What are you using to test your water parameters? they appear to be fine/happy.
as long as i keep a watchful eye on everything and do frequent water changes will everything be ok? You will have to keep up with daily water changes until your tank is properly cycled. Don't forget to properly treat your fresh water with the appropriate water conditioner for your tap water conditions.
also, i'm picking up a fluval fx5... i don't really like the HOB filter. i may keep it in addition to the fx5 for the circulation.