Hi Mate - lots of things to consider, the main thing to consider is what kind of tropical fish you will keep - this has an impact on the size of tank and equipment needed. For example some tropical fish grow really big so you will need a big tank, some like rocks and plants so you should build these into the tank
Have a look here:
http://www.fishforums.net/
and here:
http://www.tropicalfishforums.co.uk/
Pay particular attention to 'new tank set ups' as its not as easy as putting it all together and bunging some fish in, you have to 'mature' the tank medium, check ph etc and ensure the water is correct, make sure you introduce fish SLOWLY and add hardy varieties first