If it were my deck, I would try and replace a few of your 1-time sacrifice abilities with permanent sac outlets. I agree with you that you may be (significantly) too high on board theft, playtesting in your group will be critical to see how fast you run out of targets and have dead cards in your hand. If you do go with more GY theft, I would highly recommend
Altar of Dementia. This would also pair very nicely with a
Rise of the Dark Realms as a finisher.
If you're married to The Beast as your commander, respect, but I would think for this plan to really succeed, getting a GRIXIS commander to give you access to blue perma-theft and artifact theft would probably step you up a level in competitiveness. Take and keep the really good stuff (including other people's commanders) and steal and sac the other stuff to take away blockers and get sac value.