I have a snowflake eel and a scorpion fish in a 35 gallon. Neither is big enough to feel confident in attacking the other. They get along fine, although the eel is hyperactive at night, and I've caught him following my fish around, harassing him by getting too close. I feed both at the same time (thawed krill shrimp w/ tongs) + they do not fight when feeding either.
I introduced the eel by putting him in a glass jar w/in the tank so they got used to seeing each other. I also set up a hiding place for the eel which the scorpion fish can't enter as a precaution. I also fed both about 20 mins before releasing the eel.
They are an odd couple, both in personality and appearance.
I'll keep my eye on them as they grow-- at some point I may have to split them up.
Hope some of this info is helpful + best wishes on your new tank!