"I still haven't heard an explaination for why we're supposed to eat fish on Fridays that made any sense."
This is an explanation: meat is expensive; in the past it was often prohibitively so. Christians who had the means to afford meat for their daily meals were asked to give it up on one day a week, that is, on the weekly celebration of Christ's death each Friday. They were then asked to donate to the poor the money that they would have spent on the meat. This was, and still is, considered to have two benefits: the Christian can to a very small degree identify with the self-giving of Christ by making a personal sacrifice (by not indulging in tasty meaty goodness), and by providing for the less fortunate (giving the funds to the poor), all in one act.
Why fish then? Fish was substituted as a less expensive alternative to the more expensive beef, pork, or poultry, so that the Christian could still have a healthy meal in his or her diet on Friday. Recently this practice has been relaxed (except during Lent when it is still required), so that the Christian can come up with his own penitential act each Friday.
Whether you agree with this practice or not, I don't think you can deny that it makes at least a little sense. Also, this might help: imagine a similar practice in another culture of which you are less critical than you are of Catholic culture (Native American spirituality, Buddhism, Islam, etc). You'd probably not criticize it so readily; in fact, you'd probably have praiseworthy things to say about it.
"Hell, go to a Catholic mass for once. It's all "Stand, sit, stand, kneel." It's like the priest is a gym teacher putting the parishioners through calisthenics."
Again, an explanation: Catholics and Orthodox Christians, much more so than Protestants, hold that we are spiritual AND bodily beings, and that we pray not only with our souls but with our bodies. Your posture (i.e, bodily position) is the way to pray with your body. Similar to the way that you stand in a courtroom to show respect to an entering judge, or the way that you go down on one knee when you propose to a woman, what you do with your body is an outward sign of what you're doing with your soul. The Catholic Mass is full of various "postures" of the soul toward God and toward your fellow congregants, and the bodily postures are designed to be signs of these inner dispositions. It seems like calisthenics to an outsider, but when understood rightly it is quite beautiful.
Again, you might not agree with all the sitting, standing, or kneeling, but you asked for a reasonable explanation, and I've tried to give one. I'm really not trying to be antagonistic here, just to explain the things you've asked about; I hope it helps you to be a more informed Catholic.