#All the way down (it works*)
All the way down (it works*)
As you've thought, there is nothing in this that creates any rules issues.
You've hit the pertinent points:
- Any creature can attune to the Ring of Spell Storing
- They still need to spend the hour and be able to do so. But, but the 6 INT should allow for that for Steeds and commanding the familiar should work the same way.
- Whomever is attuned, including beasts, to the Ring of Spell Storing can cast a spell from it:
While wearing this ring, you can cast any spell stored in it.
- Find Familiar, Find Steed, and Find Greater Steed are all 5th level spells or below and viable to be stored in the ring.
Any creature can cast a spell of 1st through 5th level into the ring by touching the ring as the spell is cast.
This shows that your belief that this should work is in fact correct.
There is one problem
##There is one problem YouYou personally can't have Find Steed and Find Greater Steed going simultaneously. Find Greater Steed explicitly states:
You can’t have more than one mount bonded by this spell or find steed at the same time
However, that just limits your starting set to 2 creatures and they can do this again. You just don't start with three.
A DM's option
##A DM's option HavingHaving said that, the DM can still put the kibosh on this if they feel it's taking away from the table or other players. One player having a huge array of creatures at their disposal may cause issues with other players to the point where it becomes unfun. That's going to be up to the table, the players, and the DM.
*The only issue to really consider is if the animals have the right appendage. It's important to note that if you do use polymorph to get around that, then the creatures will lose their intelligence and drop back down to whatever the new stat block says it is. A DM can rule that creatures of low enough intelligence aren't able to understand how to utilize the magic item or be able to maintain concentration for the casting durationsduration.