Setting up the fish tank

Fig. 1

Introducing our Fish tank! 
Friends and people who know me... please don't think that I have forgotten about dogs. Its just not time yet for the dogs.   
This is our first pet venture other than my Dog Care and Training Center for undergraduate architecture thesis. 
23rd December 2011, we were at Sanket's place for dinner and fell in love with his fish tank. He's our "mentor", you can say "Guru". First day of Christmas holidays and we were at Petsmart and Petco trying to get the best deal for a little fish tank. I wanted something "small", that I could lift with my hand and may be with one Goldfish in it. We came home from Petco with- 15 Gallons - Tetra Tropical Community Fish tank with a light, heater and water purifier. Gravel to fill the bottom of the tank. Sid and his family joined us and bought the same! 

Fig. 1.2

Fig. 1.3 (Plan View)

 My questions:

1) Do fishes like colors? do they respond to shape and texture?

2) How will I clean the tank?

3) Will they have enough hiding space? or if they hide, will I still be able to see them?

4) and of course the Cost??

My thought- 15lbs of gravel same color and fill the tank with colorful fishes and green artificial plants. Easy to clean and maintain. 

My client (my hubby who was paying for it) here, wanted something colorful and filled with pebbles and shells. 

This was out final output: 

Fig. 1.4 (Front View)

15lbs of gravel, 5lbs of red gravel, 5lbs of blue gravel, with some decor on the right bringing in the shells and on the left some rock with moss on it! (all artificial ornaments from Petsmart) Dark pebbles to add some contrast. some green plants and a piece of Roman sculpture to add the effect of archaeological remains underwater. We added a thermometer for the temperature control. Ah yes and then a glass bowl from Michael's to give them the feeling of "A fish in a glass bowl".