I've replied about the eel on your other thread, but honestly, your stocking is pretty bad.
Gouramis and Siamese fighters shouldn't be kept together; they're quite closely related and often fight. The kuhli loach would appreciate being in a larger group (6+), always assuming your eel doesn't eat them overnight...
The plec is very, very likely to outgrow your tank pretty rapidly; do you know what species it is? They do vary so it may be alright. If you can post a pic we'll identify it for you.
How long has your tank been set up, btw? Was it cycled at all?