Your clever cat sounds like our Whisper. He is very intelligent and loves to explore (fortunately he tolerates a harness and we either take him outside with it or under strict supervision). He also knows what doorhandles do, but fortunately can't operate them himself.
As for food fussiness, our cats amuse us too. There is a wet food brand called "Fussy Cat" here that Tabitha won't eat at all and Whisper only under protest (and he's the food-oriented one). Tabitha definitely prefers anything fish, even to the extent that she'll voluntarily go to her dry food feeder (containing salmon-flavoured kibble) instead of eating the chicken or beef wet food. As for the loaf type foods, I don't think she even recognises them as being edible! Fortunately Whisper has not worked out that human food is edible (and we plan to keep it that way), or he'd be intolerable at meal times.
Are you sure he's actually dumb if he's easy to train? One of our cats definitely cries when she really wants to play, but it's because she wants me to go to her rather than her walking down to the other end of the house where I am!