A Message Of Encouragement

Question

_{This puzzle is part of the Monthly Topic Challenge #8: Cellular Automata.}

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This themed cryptic puzzle is dedicated to a user (from another website) who proposed to make March 23rd as a special holiday for his group after seeing one of my other questions on Puzzling.
Unfortunately, he got bullied and hacked about two years ago and became much less active.
This puzzle also contains an encouraging message for him. If he succeeds in his work, then we can probably confirm the validity of the hidden word.
Best wishes to him, and our fellow puzzlers!

Solve the clues to find the 16 words/phrases.
The 16 words/phrases below may be separated into 4 groups.
Additionally, there is a six-letter word absent from the wall which, I hope, will be able to fit in all four of those groups in the future, and that is the hidden encouraging message.

• Football Player is Street Queen (7)
• Start - up, left, down, right - In Cored Cannon Pot (8)
• Glue rash in most of eye (5)
• Calculate 2³ towards ∞ (6,5)
• Cunning of turned chromosomes (4)
• Author of The Necklace Young Man (3)
• Part in lethal fight (4)
• Detective from southern part of Stockholm encounters swimmer returning (6)
• Likely to spread infinity City Time notes (10)
• Upwards dark, not front or back (3)
• Dorothy messed about a Game Of Life book from church (9)
• 1103M below ordered veils in a bright color (6)
• Heartless spy going around a long distance XD (6)
• Semi-valued Kentucky car: That is one of Odin's 12 (8)
• The Sixth Formerly prohibited country's biological weapon (5)
• Pale hardware in Wyoming (4)

- - - And Farewell To Biological Weapons!

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Task: Complete the connect wall and find the hidden word.

Optional task: Can you guess what his favorite song is? Please answer in comments. He asked me this question , which I couldn't answer.

Hint 1:

Three of the four categories are related to cellular automata.

Hint 2:

Click here or here

Hint 3:

The words "Bottle" and "Pyrotechnecium" belong to one of the categories.

Hint 4:

The words "Bell", "Grant" and "Summers" belong to one of the categories.

Answer 1

The word you are looking for is

GALAXY!

Clue Answers:

Football Player is Street Queen (7)
BLOCKER (BLOCK+ER)
Start - up, left, down, right - In Cored Cannon Pot (8)
CAULDRON (CA+ULDR+ON)
Glue rash in most of eye (5)
EPOXY (E+POX+Y)
Calculate 2^3 towards ∞ (6,5)
FIGURE EIGHT (2^3 calculates to 8)
Cunning of turned chromosomes (4)
FOXY (OF< + XY)
Author of The Necklace Young Man (3)
GUY (double definition)
Part in lethal fight (4)
HALF (letHAL Fight)
Detective from southern part of Stockholm encounters swimmer returning (6)
HOLMES (HOLM+E+S)
Likely to spread infinity City Time notes (10)
INFECTIOUS (INF + C + T + IOUS). Not sure about the E; MOehm notes EC could clue city for a Londoner.
Upwards dark, not front or back (3)
MID (DIM<)
Dorothy messed about a Game Of Life book from church (9)
ORTHODOXY (DOROTHY + XO), scrambled (XO may refer to cells on/off? Not sure)
1103M below ordered veils in a bright color (6)
SILVER (R follows VEILS scrambled. R is a Methuselah pentomino that stabilizes in 1103 generations)
Heartless spy going around a long distance XD (6)
SMILEY (SY around MILE. XD is an emoji.)
Semi-valued Kentucky car: That is one of Odin's 12 (8)
VALKYRIE (VAL + KY + RIE) (Not sure why RIE is CAR. Maybe aRIEs, semi-cut like VALue)
The Sixth Formerly prohibited country's biological weapon (5)
VIRUS (VI + RUSsia)
Pale hardware in Wyoming (4)
WAXY (AX in WY)

Note: They were alphabetized, which assisted with solving.

The Groups:

Words ending in ‘XY’
EPOXY, FOXY, ORTHODOXY, WAXY
People who have discovered a Game of Life Oscillator
Richard GUY
Stephen SILVER
Entity VALKYRIE
Rich HOLMES
(Hint: Bell, Grant, and Summers also are GOL’ers)
Game of Life Oscillators
SMILEY
BLOCKER
FIGURE EIGHT
CAULDRON
(Hint: Bottle and Pyrotechnium also fit)
Rules created for the Game of Life, that end in ‘Life’
HALFlife
MIDlife
INFECTIOUSlife
VIRUSlife

Final Connection:

GALAXY (6)
- ends in ‘XY’
- Kok’s GALAXY is a Game of Life oscillator
- GALAXYlife is a Game of Life rule
- Person: No one at this time (hence the "I hope in the future"... see next paragraphs.)

Theme: Regarding 3/23, encouragement, and weapons. I thought Reagan’s Star Wars fit more to the theme, but now that seems unlikely.
Instead it would appear your friend is a web user who goes by “colorfulGALAXY”, so your message of encouragement is that in the future, they discover a GOL oscillator, thereby adding their name to the “final connection”! As of yet, it seems their main claim to fame is having their username associated with “contributing” to the XKCD wiki with the song “Justice” (not sure if this was by them or more likely the referenced hacking).
But with the specific inside knowledge to deduce this, and the vast amount of material in the GOL wiki, this puzzle seemed hard! The hint that 3 groups were restricted to GOL knowledge helped a lot (and the links).