How many discus could go into a 75 gallon tank with 6 angelfish and assorted tetras?

So i am getting a 75 gallon for my birthday on June, 12 and i am getting 6 baby angelfish and some assorted tetras like serpae tetras or neon's. What is the average price for discus and if it is too much, what are good fish to go with the angels and tetras. What other ones are pretty and peaceful fish that will get along. Also what is a good algae eater. Could i have any plecos? I don't want any bristle nose or rubber lip ones. I would like to have a common pleco. If i can't then please list other pretty ones that will go in there. Thanks??Any other stocking suggestions are welcomed.