Lots of name references here! Didn't pick the double definition of 4D without looking it up. Never heard of 6D. Everything kind of came together pretty well, really.

Across

1

Levelled off but not disposed? (11)
DISINCLINED — cryptic def.

7

Shoot a fellow (3)
BUD — double def.

9

Prosper and start to bear defeat with honour (7)
BLOSSOM — B (first letter of bear) LOSS (defeat) OM (honour)

10

Sees last locks? (7)
BEHOLDS — BE (last) HOLDS (locks)

11

Empty talk about the Spanish Celts (5)
GAELS — GAS (empty talk) around EL (the Spanish)

12

Novelist is starting to burrow into two measures of cloth (5,4)
ELLIS BELL — IS B (first letter of burrow) inside ELL ELL (two measures of cloth)

13

A brooder in republic on hill (9)
INCUBATOR — IN CUBA (republic) TOR (hill)

16

The writer, about to have hesitation before a woman (5)
ERICA — ER (hesitation) I (the writer) C (about) A

18

Put garment on right to dance about (5)
CAPER — CAPE (garment) R (right)

19

Manage to kick all over (4-2-3)
HEAD-TO-TOE — HEAD (manage) TO TOE (kick)

21

Abundant? Brimming by the sound of it (9)
PLENTIFUL — homophone of PLENTY FULL (brimming)

23

Sign the lavatory has no-one in it (2-3)
TO-LET — TOiLET (lavatory) with no i (one)

25

Poor Jane's in second. In first is a dog (7)
BASENJI — B (second) I (first letter of in) containing anagram (poor) of JANES

26

Good football year before making cheese (7)
GRUYERE — G (good) RU (football) Y (year) ERE (before)

27

Never away outside with a woman (3)
EVE — nEVEr (without outside letters)

28

Deckest York out thus? It's risen fast! (11)
SKYROCKETED — anagram (out) of DECKEST YORK

Down

1

Remove faults from French spirit (5)
DEBUG — DE (from French) BUG (spirit)

2

Exhibitor with better water-repellant cover (6,3)
SHOWER CAP — SHOWER (exhibitor) CAP (better)

3

Sniffs no hot eats (5)
NOSES — NOShES (eats) without h (hot)

4

Constant unit of brightness? (7)
LAMBERT — double def.

5

Faint and misty, unable to change by the end of winter (7)
NEBULAR — anagram (to change) of UNABLE, R (last letter of winter)

6

Bursting open modern centre with the fellow's money (9)
DEHISCENT — DE (middle letters of modern) HIS (the fellow's) CENT (money)

7

Some unbeliever to be false to (5)
BELIE — hidden in unBELIEver

8

Offend poet laureate in disorder (9)
DISPLEASE — DISEASE (disorder) containing PL (poet laureate)

13

Helpless old Peruvian? Quietly, talented (9)
INCAPABLE — INCA (old Peruvian) P (quietly) ABLE (talented)

14

Singers exclude it on extra song beginnings (9)
BARITONES — BAR (exclude) IT ON ES (first letters of extra song)

15

Verse concludes episode (3)
ODE — last letters of episODE

17

Good thinking, let client out (9)
INTELLECT — anagram (out) of LET CLIENT

19

Vigorously call about lift construction (7)
HEFTILY — HEY (call) around anagram (construction) of LIFT

20

Most declare without proof, or return briskly (7)
ALLEGRO — ALLEGe (declare without proof, without last letter) reversal (return) of OR

22

Pearls. No standard, that is, for a woman (5)
ELSIE — pEarLS without par (standard) IE (that is)

23

Boot the main body (5)
TRUNK — double def.

24

Pace and skill rises with energy in degree (5)
TREAD — reversal (rises) of ART containing E (energy), D (degree)