If one of the "yellows" is a hybrid (and I suspect it is), you won't really know what the personality is until it reaches sexual maturity. However, from what I've heard most of the lab x estherae crosses are pretty peaceful.
Why do you think you need an extra sponge in the tank? If you have a filter running (and I'm assuming you do) all the bacteria you need will grow in it. You also have a smaller amount of bacteria on every surface of the tank (ie gravel, rocks, etc).
I'm sure they like swimming against the current. I have two filters running on my tank and they do seem to enjoys the resistance, just as long as you have plenty of rocks for them to get out of it when they need to. Juveniles especially will get worn out constantly swimming against the current.
Your cichlids will certainly enjoy vegetables. Peas, zucchini, spinach, other greens (iceburg doens't go over very well IME), and cucumber. I prefer to freeze them first, and then let them thaw, that way they are nice and soft. However, you can take fresh veggies and parboil them, then let them cool. Peas are a little different, you need to boil them, or heat them up in the microwave. Then split the outer shell and squish out the inside, and throw out the outer shell. The fish can't digest the outer part, but will go crazy over the inside. Don't be surprised if the labs just pick at the veggies, mine are never too interested though they will eat some. If you can get spriulina enhanced brine shrimp your labs and estherae will love you for the shrimp and the spirulina will add veggies to their diet. I'd only feed them that once a week though, because the kenyi can't handle too much animal protein.
