Your tank is ample size for angelfish.
Angelfish and Plecostemos should get along ok, since plecos usually keep to themselves. Most people keep them together with no problems.
I personally will not buy angels that young. They don't last long unless your water is PERFECT, they catch diseases easily, plus most other fish will bully them. I always buy older angels.
Also, the store is wrong, they are called Angel Fish (Pterophyllum scalare), not Angle Fish.