Consider myself to know relatively little but could go on with heaps off the top of may head.
Some basics
A few gold fish (cold water type) are simple & cheap to maintain ie small bowl or tank, more and more of them the maintenance and cost increase.
Tropical fish require a balanced environment, maintaining correct tempt and water quality is vital (Take note climate change sceptics). It is possible to add a verity of species of fish ect to help maintain the correct balance and minimise maintenance but you need to keep that in control.
have see some amazing aquarium displays, don't know what effort and cost goes into them but dam sure it's not just plug and play
