Not pregnant or bloat I don't think...just a fat little fish, lol.
Never seen that, hard to find the little buggers in the dark though.
I believe they like to be in a group of 3 or more,they definitely interact with each other a lot. I've heard 30 gallons as the recommended minimum and they thrive in heavily planted and established tanks.
I wouldn't give up yet, mine took a few tries to realize it was food, especially the zucchini. And they also don't always park themselves on top of the wafer, they kind of hang out around it catching the debris that falls off.
it depends on the breed of otos you want to buy cause there's so many.the ones i have only grow to be about an 1-1 1/2 inch long. it is the one in the far back of the tube