[RPG] Are there any stats or guidelines for deities’ stats

D&D 5e doesn't have a specific rule on this because the fifth edition of the D&D ruleset doesn't make use of 5' squares when determining positioning of creatures -- it relies more heavily on an abstraction of what is happening mechanically in the game to determine this. Note that there are variant rules in the DMG for using a grid where 1" square = 5' square.

That being said, what we do have is a general idea of what space a creature of a given size "controls":

Size       Space
Tiny       2½   by  2½  ft.
Small       5   by  5   ft.
Medium      5   by  5   ft.
Large      10   by  10  ft.
Huge       15   by  15  ft.
Gargantuan 20   by  20  ft. or  larger

Source: 5e SRD pg 92

And just below that, in the SRD:

A creature’s space is the area in feet that it effectively controls in combat, not an expression of its physical dimensions. A typical Medium creature isn’t 5 feet wide, for example, but it does control a space that wide. If a Medium hobgoblin stands in a 5-foot-wide doorway, other creatures can’t get through unless the hobgoblin lets them.

A creature’s space also reflects the area it needs to fight effectively. For that reason, there’s a limit to the number of creatures that can surround another creature in combat. Assuming Medium combatants, eight creatures can fit in a 5-foot radius around another one.

Because larger creatures take up more space, fewer of them can surround a creature. If five Large creatures crowd around a Medium or smaller one, there’s little room for anyone else. In contrast, as many as twenty Medium creatures can surround a Gargantuan one.

Based on the amount of space a tiny creature takes up (2.5 x 2.5, or 1/4 of a 5 foot square) I think it's safe to say that the breakdown is the same as in previous editions -- you could fit four 2.5' squares inside a single 5' square, so you could fit 4 2.5' tiny creatures in the space occupied by a creature who occupies a single 5' area.

However, I think it's important to remember that things are not often so neatly organized into 5' squares, and that's one of the reasons grid-based combat in 5e is a rule variant and not the base assumption. Allowing combat and positioning to occur more organically might be a bit more work than using a grid system but in my experience it has allowed for much greater creative freedom from players.

I know of no official conversion, as of writing. However, were I to write a conversion, I would begin by comparing the stats from D&D 3.5, where the astral dragon appeared in Dragon magazine issue 344. I would then use that to adapt an existing 5e dragon (which for copyright reasons I won't replicate here).

The astral dragon is approximately as strong as a brass dragon of similar age, and we can use the 5e statistics for that as a basis, modified as follows:

• Breath Weapons (Recharge 5-6).
  • Scouring Dust. A cone of scouring dust (as the standard dragon's breath weapon, except that the damage type is slashing).
  • Psychic Wind. A 5 foot wide line of dark cloud. Affected creatures must make a saving throw or be affected by psychic wind, as per the Dungeon Master's Guide p. 48.
• Severing Bite. On a critical hit with its bite attack, the dragon instantly severs an astral traveler's silver cord, killing them instantly.
• Detect Extraplanar. The astral dragon has advantage on Perception checks made to detect creatures who are not native to the astral plane.
• Lair Actions. An astral dragon makes its lair on some chunk of matter floating in the astral plane, often the massive petrified body of a dead god. On initiative count 20, the dragon causes one of the following effects:
  • All gravity within 60 feet of the dragon is nullified. All creatures' standard walk speeds are reduced to 10 feet, and creatures in the air who lack a fly speed simply float in place.
  • Astral wind buffets all creatures within 20 feet of the dragon, pushing all creatures 20 feet in a direction chosen by the dragon.
• Regional Effects. The region containing a legendary astral dragon's lair is warped by the dragon's magic, which creates one or more of the following effects:
  • Psychic Wind. Creatures approaching within six miles of the dragon's lair are affected by psychic wind (DMG p. 48).
  • Tidy Nest. If a creature not native to the astral plane is slain within 1 mile of the dragon's lair, its body is banished back to its home plane. There is a 20% chance it will be sent to another plane. Any gold or magic items the creature was carrying are not banished.

Astral dragons are always of Neutral alignment. They consider themselves guardians of the Astral Plane, and consider all non-native visitors to that plane equally their enemies.