Can someone explain the asterisk in the "30 ft (5 ft *)" for Range/Area?

It means the HAND takes up a 5 ft area itself and you can make it reach for any creature in a square next to the hands square. The 30 ft is the area the spell has effect, which means that you can move the hand to any square within 30 ft, when the hand arises at a new location, it again takes up one 5 ft square and can likewise attempt to grab any creature in a square next to it's new location.

It doesn’t specify if subsequent strength checks are an action or not, is it safe to assume it isn’t an action to try and break out?

It's says in Xanathar's Guide book that it takes an action to try to break out. DnD Beyond forgot to include that piece of info, and should amend the spell asap. 

Does "reaching for a different creature" include moving to a new spot within reach? So far I've interpreted it as either grabbing or moving (taking one action each), but some of the comments made me think maybe "reach for" means the hand drops into the ground, rises out of the ground next to the new target and tries to grab it (all within one action).

I would guess that reaching for a new creature within range would mean it can move to the new location and attempt it's restrain as long as it is within it's originating 30ft. and can reach the target creature at the new location. The added "...or move to a different unoccupied space..." is likely there for more tactical reasons.

You choose a 5-foot-square unoccupied space on the ground that you can see within range.

The 5-foot-square is the (5ft*) and the range is 30ft.

This means if you're trapped in a 10x10 room with 3 other creatures on a traditional battle map grid, you can't cast this spell.

As this occupies a 5' square, can it be used to flank an opponent - assuming they are the target of the spell with an ally?

Because a spell is not an allied CREATURE, it cannot be used for flanking. However, the restrained condition imposes disadvantage on the restrained creature’s attack rolls, and advantage on any attack roll against the restrained creature, which is better than flanking.

missing the action to make the strength check!

If you are fighting a single opponent and they make their initial saving throw, can you have the hand reach for them again on subsequent turns?

I assume the answer is yes, although the text at the end of the spell says “As an action, you can cause the hand to reach for a different creature...”.

can this be use to restrain a large or huge creature?

"To break out, the restrained target can use its action to make a Strength check against your spell save DC. On a success, the target escapes and is no longer restrained by the hand."

Interesting, no mention of spell ending if someone frees themselves, so you're free to move it to different target in that case, without recasting.  And there is no target size limit.  This spell just went up in my estimation.

I love this spell!  It takes up space (great for chokepoints, or to prevent reinforcements arriving), and it doesn't go away just because a target makes it's save.  It does take the caster's action to keep using it each round, but since it causes damage *and* restrains its target (any size!) - which grants all the other PCs Advantage *and* causes the monster to have Disadvantage and no move - this is well worth an action.  And a Sorc can just use Quicken to cast some other spells on subsequent rounds - full spells, not cantrips, because using your Action to control the Hand is not a "spell".  This spell allowed us not only to kill Venomfang in LMoP, but do it without suffering a single point of damage!  (Okay, VF did manage to finally break free and fly away, but an upcast sleep spell took care of that...)

My questions though:

1) Can allies shoot through/past the square the hand is occupying?  (We had our Artificer using it as a melee blocker as he flamethrower'd ghouls from behind it...)

2) Can this spell be "Twinned" using metamagic? It is technically a single-target spell, and the second hand can be used to target a different foe, so it *seems* to work in the RAW...

1. I would guess the hand would grant half cover or 3/4 cover to any creature directly behind it.  You could try to shoot past it subject to those conditions.  (I'm not a real rules lawyer, I just play one on TV.)

2. I'm pretty sure this spell can't be twinned.  The target is an unoccupied 5-foot square, not a creature.

Quote from xMugetsu13 >>

I would guess that reaching for a new creature within range would mean it can move to the new location and attempt it's restrain as long as it is within it's originating 30ft. and can reach the target creature at the new location. The added "...or move to a different unoccupied space..." is likely there for more tactical reasons.

 I think the hand can only reach for a new creature within 5 feet.  If there are multiple creatures within 5 feet and one escapes, the hand can grab another one.  If the hand has to move to get to another creature, it can't grab that creature on the same turn.

I like this spell, but it is kind of a noobtrap. 

The first cast is great and the damage each turn plus restrain is good too, but after that the fact that you can use the action to MOVE the hand will cost many newer players to waste a turn thinking that means you can actually grab something else. 

Its better to just let go of the spell as soon as noone is in range any more, since afterwards you wont be able to grab anything you have to move towards since they can just step away in the turn it takes the hand to get a second action to grab. 

it does say that they can use an action on their turn to make a str save.

The fact that you can only attack OR move with the hand really kills this spell.

Do spells always use up components or are there some spells that can reuse their components?

I’ve only watched up to episode 2x22 of critical role but so far Caleb hasn’t had to remake or buy a new hand component for this spell. At least not on camera.

In short: can I cast this spell as much as I want as long as I have spell slots for it or no?

Quick reply greatly appreciated. Thanks in advance!