It's a good idea to set your tank up a few weeks in advance, gravel, filter, heater and most importantly plants. This will get the chemical and oxygen levels settled before you put your fish in. If you're going to have any decent size of tank you'll need a good external filter.
I personally would start with small fish as you can have more fish and more variety. There are loads of varieties of tetra, danio and guppy, these will give you great colour variety. These are middle feeders so get some bottom feeders too like corydoras - again many varieties to choose from. Pleco's are great aswell as they suck on the glass and eat the algae growing there, only 1 or 2 of these though as they grow very large over time. Loaches are also nice and different but again some species (weather loach) grow quite large, I think clown loaches are a smaller variety.
Tropical fish are a great hobby, go for it, you'll love it.