I personally wouldn't leave him by himself... loaches seem to be much happier in a larger group. I'd say minimum group of 3... prefferably a group of 4-5. Now, I don't know if a 29g has a large enough floor space for 5 yoyo loaches, especially once they begin to fill out to their adult size. (4"-5" average, some say 6"+) I'm going to take a stab in the dark and guess that your yoyo loach doesn't seem to be really active, and that he was laying on his side during the day? My clown loaches are almost constantly on the move during the day, always swimming around with eachother, playing with eachother, and searching for more food. (they're little pigs I tell ya... lol) They do lay down from time to time, but mostly at night, and they all lay together to sleep. (which I think is really cute to watch) I'm willing to bet that you'll see your yoyo loach become much more active and appear to be much happier if he had at least 2 more members of his own species.
As far as your snail goes, I'd certainly agree with everyone else in that your yoyo will eventually discover that the snail is edible and begin picking at it. Once he gets a little bigger he'll probably end up trying to eat the amano shrimp also. (my clown loaches will eat ghost shrimp)
One other thing which hasn't been mentioned yet, and I hate to sound like a butthead, but you may want to consider something larger for the gold nugget pleco if you haven't already. They're a smaller species than the commons, but they'll still hit 12"-14" when full grown. You're looking at needing approx. a 75 gallon tank for him, which I'm certain your yoyos would go nuts for. With a 75, you could also increase the school size of your cardinals and rummy noses to 10-15 each. (I've got 10 cardinals in my 55 now, and they are already much more comfortable and willing to go for food than when I only had 5 of them)
