I'd say yes, for a few reasons. First - because I've had the same though, b) it would actually be quite limited due to needing an action to move, and fig 26q - it's creative!
The text of the spell doesn't specify the hand has a size, therefore it can be reasonably assumed to be "big enough" to do the task it is given, provided its within all the other parameters.
The hand is also spectral, so not a physical object. Therefore the hand itself can't be hit be attacks (unless magic weapon I think).
The hand only moves when you make it move. So unless it's being hit with a nat 20 attack, it stays within the square you put it in. It can wobble, spin a bit, be shoved out the way, but ultimately re-centers itself. If your DM says it gets blasted off because o force of the attack, then that opens the argument as to why PCs don't get thrown around when struck. Narratively you can be staggered, knocked about etc be attacks, but unless an ability specificly states, you don't get moved out of your square.
I shield can't protect you if it's not between you and the thing trying to hit you. I'd rule that unless the shield is within 5ft of the person it's protecting And is in the path of the melee attacker, no bonus AC. For range attacks, it would need to be in-between the target and the attacker, on a straight line (or close enough if angles and grids get tricky) between them. Range from you doesn't matter so long as it's still within 30ft of you.
Other than that, get creative! Have two shields for +4AC for a round or two!
Have the party stay within your movements range of the shield, ready an action for "if a member of my party gets attacked", and suddenly provide them with bonus AC!
Work out a tactic with your archers and ranged casters to provide cover for them. Shield planted in the ground, floaty shield above that with a small gap in between, become a pillbox!