The medications you listed are appropriate for those with coronary artery disease, and should have little interaction with each other. Some of these medications should be uptitrated by his cardiologist to allow for the maximum dose as he tolerates them (namely, Ramipril and Metoprolol). His Plavix should continue for either several months up to 1-2 years depending on the type of stent he received at the time of his percutaneous coronary intervention (bare metal stent vs. drug-eluting). As with most medications, daily compliance with all of these is imperative for maintaining healthy cardiovascular fitness.
Did your dad get a drug eluded stent? If so, he should be on the plavix for at least a year. I have a stent since 2006 and my Cadiologist said I have to take it indefinitely. I can only go off it for surgical procedures and then go back on it again. Maybe when the doctor answers your post he may mention this also. If he's on a bare metal stent then I think it should be 3 months. I'm not sure though. I think I may have read it on the heart forum.
I'm only speaking thru my experience w/drug eluded stent. I'm certainly no expert.
Best wishes for your dad.