If you are getting I big-ish tank 120 would be very good for a snowflake eel they add a lot of personality to the tank and make it a little different I love my snowflake on the downside you won't be able to keep smaller crustaceans but fish should be fine and they are very easy to keeep don't be intimidated
I am new to the Hobby myself 2 months and I've learned from a ton of mistakes. I think the biggest mistake I learn from is going small on my tank I think you have a great size in mind and you'll love it once you're in it.