Buying Oscars is there a difference besides the colors e.g: temperament, diet

They are all the same species, just different color morphs (or I think that's the case), so you really don't have to worry about crossbreeding. You plecos should be fine, just make sure they have places to hide. Oscars are on the low end part of the cichlid aggression scale. You might want to start with more than 4 small fish and grow them out and keep your favorite 4.

All are the same species they are just line bred (like dogs) to get the more attractive colors. If you start off with four you might get a pair. I wouldn't worry about the plecos unless the oscars pair off and then everyone will probably need to be removed.

I sugguest you buy 2 oscars only since you have 150 gallons tank. Oscar grows up to 12". They need room to turn and swim. 4 will be crowded for them.

Oscar is very sweet temper unless it is feeding time or breeding. My oscar lives with my Blood Parrots, Severums, Firemouth, Chinese Algae Eater, and Loach. He loves hanging out with my Blood Parrots. However, he gets aggressive when it is feeding time. My oscar went after my baby severum because he thought that my severum was stealing his food. Just don't leave any too small fish that can fit in oscar mouth. Otherwise, your plecos should be find...I doubt they can fit in the Oscar's mouth.

Oscars are all the same, just the colors. There are called Purple, Albino, Tiger, Red, and couple other colors that I couldn't think of now

If you need more info on Oscar, check this site out.

http://kingsoftheaquarium.tripod.com/oscars.htm

Good luck telling the difference between sexes for oscars. There are 2 ways :

1. vent the fish

2. wait for 2 to pair up and see which one lays the eggs.

yea oscars are very hard to sex easiest way is to let them pair up, since i dont know how to vent them. but yea 3 is the max for a 150g, but i would go with 2. if you can sell them back to the LFS then you may get 4 or so, but i dont recommend it, cause i got screwed from LFS' once with my pacus, that were said to be silver dollars when i was inexperienced and now the LFS says no they wont even take them for free, and im still trying to find a home 4 them cause i cant release them into the wild.