Peregrination is a classic budget card that both me and Mark's deck use in our decks since it's a four-mana Cultivate or Kodama's Reach with a scry attached
The first secondary commander is Rayami, First of the Fallen, who plays into the creature-exiling profit whenever the exiled creature has basically any static ability by bestowing said creatures ability onto the keyword-thirsty vampire
Inga and Esika, Morophon, the Boundless, Tesak, Judiths Hellhound, Magnus the Red, and Rakdos, Lord of Riots can all make a massive impact on how fast your army grows
When the last [soul] counter is removed, sacrifice CARDNAME and return the exiled card to the battlefield
These work pretty seamlessly as a fusion between the two card types
Talk about a win-win