Fish can be a pain to catch, no doubt! Get a big net and leave it in the tank for an hour, and then come back and use just your hands to chase the fish into the net. It won't be scared of it if you've left it in there for a while.
Pearl Gourami, a pair. Not a trio, the stronger 2 will bulky the other. Golden Womder Kili, the are nice. Not too big, not mean IME, and very easy to catch. I could pick mine up in my hand.
Cardinals might not work well with Diamonds!
Sent from my bed, the only space available to me that isn't smothered in dirty laundry or aquariums.