I would say they have to be on the floor, but other people might disagree.
I wouldn't allow you to move the ring, no.
This is a much, much discussed topic. My personal interpretation is that the targets outside the ring aren't affected. You, inside the ring are protected against them, unless they can penetrate the ward.
The descriptions of many of the ward spells say that in the right light they look like a faint colored dome, and also things can be contained by a ring, so maybe the ward is just a semi-permeable barrier.
Perhaps a ring target is actually a shere that is defined by the circle drawn on a plane, so putting it on a wall or cieling would make it difficult to position oneself within.
Of course this brings the arguement where if the ward is a sphere then it is possible that a very tall character in a very small ring is not protected, at which point the troupe slaps your player.
I believe True Lineages uses a Ring duration spell to trap ghosts in a mirror. It can hence be argued that "cannon", or at least the deuterocanonical books, allow a "circle" to be on just about anything.
I'm not sure if I'm comfortable with that or not.
Based on the above, I would say no.
I remember someone describing a magus that used rings engraved on his talisman to trap his opponents' spirits.
Beautiful to behold but often a nuissance at their best! My jury is still out on the whole ward issue. Can't entirely live with them, certainly cant live without them.
Another somewhat undecided issue in the rules what it takes to "break" the circle? Physically destroying it, just someone passing over it, or the enchanted thing(s) or being passing over it - leaving it?
On a sidenote to this whole Ring/Circle business it is really an interesting way to make seudo-permanent effects. We had a NPC-magus that had installed a broad band of bronze in the wall of his circular tower chamber. By the use of this he had made several effects that thus remained even years after his death - and at the time of our protagonists intrusion into the former magus' sanctum - including two bronze guardians made by human skeletons incased in bronze wielding wielding Greek weaponry. Well.
I have an NPC in my campaign that is in the process of enchanting a silver circle inside of his lab for various effects (although no effects to summon demons like a couple of the players have theorized). A few of the effects are to strengthen and repair the circle incase anything happens to it, to stop it from being 'broken'. Quite a few of the effects are going to be enchanted into it, but it will also serve as a boundary for any other ring/circle effects he wants to cast in the future.
As a SG, my personal take on this would be to allow certain non-standard uses of Ring and Circle so long as a proper "mythic" feel is maintained and the desired effect doesn't come off as being just an attempt to circumvent the rules (or to apply them too literally).
For instance, I would allow a Ring to be created around a door and used to effectively create a ward that prevents something from entering through that doorway.
I do not follow the "invisible dome" concept too much, so I would not allow a ring on a wall (or around the door, in my example) to project an outward force (or sphere) that keeps something at a distance.
The opening sequence shows a wizard preparing to summon a demon. While the wizard is busy perusing over some ancient tome, going over the steps of the ritual one last time, one of his goblin lackeys is busy adding the finishing touches to the elaborate pentagram/summoning circle the wizard is going to use. I can't recall what happens exactly, but something scares/startles/intimidates the goblin causing him to loose his concentration and he accidentally steps on a portion of the circle (which is fashioned out of magical glowy powder). Needless to say he doesn't fess up to it... the wizard casts the summoning... and the demon, immediately sensing the breech with great joy, proceeds to whoop some butt.