A few items:
1) Are you putting this together for some special rules group/tournament? I say this because typically "tribal" just means that you're working to really emphasize a particular creature type, but it doesn't preclude you from using other cards. For instance, my mono-black zombie build has both Ghoulcaller Gisa and Liliana, Heretical Healer as possible commanders.
2) For what it's worth, you might benefit from looking at some of the other zombie or zombie enabling commanders out there. Jarad is good, but he's best in a more general "graveyard matters" deck than a zombie tribal build. His real strength comes from the sac ability that can nail all your opponents for increasing amounts of life. Other zombie commanders that would simply be better include: Grimgrin, Corpse-Born, Balthor the Defiled, Sidisi, Undead Vizier, the two I mentioned above, and more.
3) Do you have a budget for improving the deck? There are a wealth of relatively cheap upgrades you could order that will help make the zombies more dangerous. Generally speaking, zombies tend to be rather unthreatening 2/2s... not exactly going to get you anywhere against a bunch of 5/5 dragons or things of that nature. Adaptive Automaton, Cemetery Reaper, Undead Warchief, Door of Destinies, Endless Ranks of the Dead, etc... if you want some more inspiration look at my build: https://deckbox.org/sets/956650
4) You only really have limited interaction with opposing creatures. Like it or not, commander is a creature heavy format and you need answers, whether they come in the form of spot removal or board wipes. Thankfully, black gives you crazy access to both - see Doom Blade, Victim of Night, Grasp of Darkness, Tragic Slip, Hero's Downfall, Go for the Throat, Ultimate Price, Diabolic Edict, etc for spot removal AND Mutilate, Languish, Crux of Fate, Living Death, Extinguish All Hope, and so many more for board wipes.
Generally speaking, remember that EDH is a social format and everyone is meant to have fun, so add degenerate combos at your discretion. Balthor (as your commander) + Noxious Ghoul for recursion and repeated one-sided board wipes can make you a sizable target...
Hopefully this helps! Good luck!