If I may suggest, first plug around the members tank threads here, read some diaries of what members have gone through in their setups and try and get an idea of what livestock you would want to keep. Have a look through liveaquaria.com or other online fish sites for some ideas on what livestock you might want. Keep in mind that Fish only tanks with live rock (FOWLR) are much cheaper than full reef tanks packed full of corals and other photosynthetic inverts. Then, once you think you know what you want to keep, maintain a really open mind, and come back to ask us about the aquaria you like. Its quite possible that you've chosen something very costly, difficult, or unsuitable for your tank size so be prepared to go back to the drawing board a lot.
You're talking in kilograms so I assume that means you're a UK resident?