HELP in buying AQUARIUM - specs to look for !

PS : I have no idea reg. aquariums and fishes. Saw at someone’s house. Had a talk at home. Everyone agreed. So, will be visiting the local market in a day or two. So, what all one need to look for while buying……Noted down some queries I have…posting them down :
1>features
2>tank size
3>tank glass types,material
4>pebbles, gravel
5>fishes, their types and cheaper/costlier species of fishes, {A silly question to ask but…} how to check if a fish is in health or not
6>{Again a silly one to ask} Do we get any warranty of aquariums (tank+fishes)
7>Fish Food
8>Decorative plants(other stuff)
9>price of aquariums(in total)?

My requirement approx. -
Size – 1.5*2*1.5 (b*l*h) in feet
Fishes – 6-8 (Small ones)….Please recommend whether small ones or big ones look prettier.