Lots of words I hadn't heard of before (or maybe I had, but they didn't stick)! Even so, good clues and a bit of intuition got them in.

I struggled (and still struggle) with the parse of 3D. I'm also not sure about the implicit pluralisation of ecstasy in 18D, but it very almost feels correct enough.

Across

1

Listing preference (7)
LEANING — double def.

5

Munchers caught choppers (7)
CHEWERS — C (caught) HEWERS (choppers)

9

Estimated sound space for visitor's accommodation (5-4)
GUEST ROOM — homophone of GUESSED (estimated), then ROOM (space)

10

Trees a gust wrecked (5)
TSUGA — anagram of A GUST

11

Kind of chair to put down gently (4)
EASY — cryptic def.

12

Dismayed about monarch returning adorned (10)
APPARELLED — APPALLED (dismayed) around reversal (returning) of ER (monarch)

14

To run a hospital with the Mosaic law (5)
TORAH — TO R (run) A H (hospital)

16

Investigator Edward returned etc., mistakenly with four English (9)
DETECTIVE — reversal (returned) of ED (Edward), then an anagram of ETC, IV (four) E (English)

18

Follow to seize neckwear (3-6)
DOG-COLLAR — DOG (follow) COLLAR (to seize)

21

A man in bright-coloured garments (5)
EDGAR — hidden in bright-colourED GARments

23

Old gold piece worker finds excessive (10)
EXORBITANT — EX (old) OR (gold) BIT (piece) ANT (worker)

24

Beginning to tire of university food (4)
TOFU — T (first letter of tire) OF U (university)

27

Some nasty pestering sorts (5)
TYPES — hidden in nasTY PEStering

28

Garland certainly put together without haste (9)
LEISURELY — LEI (garland) SURELY (certainly)

29

At last, practice registered for the consumer (3,4)
END USER — END (at last) USE (practice) R (registered)

30

General-Secretary, without a weapon, flies off (7)
GLANCES — GS (General-Secretary) outside (without) LANCE (a weapon)

Down

1

Most lethargic gets oil reconstituted (7)
LOGIEST — anagram of GETS OIL

2

Declares a poem's almost finished (5)
AVERS — A VERSe (poem, almost)

3

Go within one round, in no time (4)
INTO — I (one round), then insert T (time) in NO

4

Fumbled without you, say, being banded together (7)
GROUPED — GROPED (fumbled) outside (without) U (homophone of you)

5

Radical treaty is brief (7)
COMPACT — COM (radical) PACT (treaty)

6

Firmly set in ditch by English in the finish (10)
ENTRENCHED — TRENCH (ditch) and E (English) inside END (the finish)

7

Levelling adequate fish (9)
EQUALLING — EQUAL (adequate) LING (fish)

8

Small women put on the French bandage (7)
SWADDLE — S (small) W (women) ADD (put on) LE (the, French)

13

Old Smith Bros. tossed out a clot (10)
THROMBOSIS — anagram of O (old) SMITH BROS

15

Band involved in grass got together again (9)
REGROUPED — GROUP (band) inside REED (grass)

17

Outside entertainment with a character (3)
ETA — ET (outside letters of entertainment), A

18

Doctor gets a degree in ecstasy, in the Netherlands (7)
DRENTHE — DR (doctor), then NTH (a degree) inside EE (ecstasy)

19

Not so great tell it wrong - right? (7)
LITTLER — anagram of TELL IT, then R (right)

20

Tearing right at the finish (7)
RENDING — R (right) at the finish (ENDING)

22

Railway land unknown by country's islands (7)
RYUKYUS — RY (railway) UK (land) Y (unknown) US (country)

25

Cry starts to instigate conservation of oil (5)
OLEIC — OLE (cry) then IC (first letters of instigate conservation)

26

Passive insect up in Pennsylvania (4)
PUPA — UP inside PA (Pennsylvania)