It's too small; and even if it is not, Venustus is going to get killed by aggressive zebra etc when small, and if he manage to get big, he will eat the mbunas
No he wont eat them and yes the Venustus will be fine. Venustus are gluttons and only care about eating not a very territorial fish (unless kept with other Haps or other Venustus). With that said don't feed them live or meaty foods, stick with pellets.
Your stock sounds good.....