How does the perm placement happen? We can still CC the steed after using the skill right (the steed retains HP?)?
Steed|Stallion is not immune to CC or any other effects
As for the permanent placement, that depends on coding I guess. The way I imagined it once you have a Steadfast'd Steed in play, the next time you play a permanent you could target it or the permanent rows. If you target the latter, the permanent will be placed on the slot next in order