Any permanent will do, which means there are plenty of avenues to take
Secret rare cards have a higher collection number than their set number, which is why theyre secret. Rainbow cards are considered secret rare, as they are some of the hardest to come by
If you wanted to go for the outright reanimator strategy, though, I'd stick with Chainer, Nightmare AdeptChainer, Nightmare Adept, who makes it much easier to stock your graveyard and gives your recurred creatures haste for good measure
These also have somewhat guaranteed pulls just due to the sheer number of packs
Saheeli, the Gifted is a fine commander, with her ability to add a bunch of mana with her second +1 being especially scary, but she suffers from the fact that there are a bunch of artifact-based Commanders available, including the extremely powerful Breya, Etherium Shaper, so being "fine" might not be enough to pick Saheeli, the Gifted as your Commander over other options
What affects the value of Arcane Signet