As SevenSidedDie says, there are no rules for this, so you(r DM) needs to make a ruling one way or the other.

Personally, if I was the DM on the spot, I'd probably rule that:

• Yes, the characters can totally call out "invisible goblin on my 2 o'clock, distance 30 feet!" and be understood. If necessary, they can also use their finger to point.

• No, I'm not going to quibble about whether the characters would know such tactics, or whether they'd really be appropriate for the setting, at least not without a very good reason. The characters, at least past level 1 in any typical campaign, are all highly experienced combat veterans; they'll know how to do that, or something equivalent.

• Yes, relaying the information to the other players in squares is a perfectly reasonable abstraction. Or we could just skip that bit and just assume that the other characters now know where the enemy is.

• Yes, the other characters can attack the indicated square. However, the target creature is still invisible, and thus has total concealment, so even by RAW, they'll have a 50% chance of missing it completely.

• If the target is more than, say, 10 squares away, I might even give the other characters an additional penalty to hit, because they're not even sure exactly which square the target is in. Also, unless they're using telepathy or something, the target might be able to hear the shout and take evasive action, which might merit a further penalty to hit. Neither of those is RAW (as far as I know), but I'd consider them quite reasonable rulings, depending on the exact circumstances.

• If anybody objected, I would discuss these rulings (especially the last one) with my players, and adjust them accordingly. However, I would also remind them that, whatever they can do, their enemies can do as well. If their wizard can pinpoint an invisible enemy's position exactly from 500 feet away, and relay it to the rest of the party, then so, presumably, can any intelligent enemy with See Invisible. That should, hopefully, be sufficient incentive to reach a decision that's actually more or less balanced.

No

The disk can’t leave proximity to the ground. It can manage terrain…

It can move across uneven terrain, up or down stairs, slopes and the like

… but lifting off into the air is beyond its capabilities to navigate uneven terrain. Empty air isn’t like stairs or slopes.

The disk will follow the caster within its capabilities, but breaking the bonds of earth and taking flight is not among those capabilities.

If it was, it would simply say so.