From my experience, bettas and angels are not a good idea together (which is why pretty much everyone in the aquarium hobby says not to mix them)- Before the days of the internet, I tried mixing a male betta with angels (I didn't know any better, though- nowhere to easily research, and ppl at the pet shops aren't usually that knowledgeable with compatibility) I didn't SEE any of the aggression happening at first, either- not until the very last one- but, my betta went serial killer on all of the angels in my tank, and I felt horrible about it. That is when the angels were babies- from what I understand, when angels mature, they have the potential to be very aggressive toward the betta (and are also likely to eat your guppies and black tetras), and he wouldn't stand a chance. I know some ppl have done it, but, they have a back up plan in case the stocking arrangement goes south, and can move him to another tank. When my current male betta was in my betta sorority tank, the aggression level of the females jumped up about 10 times of their normal aggressive and cranky selves, and they went after him BIG TIME, they are also super quick... can go from beautiful fins to big chunks missing in less than a second, so, you may not see it happen, and that is just when they were giving warning blows, and not seriously fighting. (again, I didn't know they weren't supposed to live together, and as soon as I found that out, he was immediately moved for everyone's safety)- Gourami and bettas will fight, so, that isn't a good idea, either. But, you already KNOW you are putting incompatible fish in the same tank together- not just with 1 incompatible species to your betta, but 2, in a tank that really isn't that large for establishing territories, that from the look of it is probably overstocked (which will up the aggression level in your semi-aggressives to begin with, as they grow)-, so, why even attempt it in the first place? Your betta is probably super stressed with that mix, which may be why he never leaves the top of the tank... Mine swim all over the place, just like any other fish would. With the mix you've got going on, from my experience, you're just asking for trouble. Make sure you have cycled back up tanks up and running to move out fish if all hell breaks loose. Good luck- I hope everything works out well, though. :\