My advice to you if you are buying unsexed juveniles is to buy way more than you plan to keep long term that way you can thin out later on for a desirable male/female ratio.
Also I'm going to agree with Pit, the addition of a Synodontis or two would be a nice touch.
Good luck with your tank, if I had it to do over again I'd go for a very similar stock list to what you are aiming for.