Thing I'm thinking is the more rams, the more likely they are to pair up, and if you end up with only one pair you could end up with the pair not being so kind towards the two left over.
Convicts, from what I read, wouldn't work at all. I don't know about jewels.
I'm not so found of neons myself, but if he would want a schooling type dither I think there would be plenty of options that are larger. Having some sort of dither would help the any cichlid he might get feel more secure and it would be more likely to come out.
And may I ask why two plecos? I myself have one bristlenose in my thirty and he is quite the poop machine. Unless he is a pleco fanatic, wants to breed them, has a frequent algae problem or is willing to clean the tank out as frequently as it might need I kinda don't see a reason to have more than one. Of course, it is a personal preference but it cuts down on the amount of fish you can stock should he want a lot of action in the tank, as plecos, while very neat fish, have a tendency not to be the most 'visual' fish in the tank. But like I said, personal preference.
Thing is the bigger the fish the less you can have, plus there is always the possiblity that it will eat any smaller fish. Just because they are peaceful doesn't mean that they won't go for something smaller when hungry. Heck, guppies will eat their own fry given the chance.
He could always go for bigger fish period, say a firemouth, pleco, and, I think, he could even pull of an african butterfly fish for the top if I'm not mistaken. It's hard to get larger show fish when you also want smaller fish as well.