This turned out to be more of a challenge than I anticpated at first; plain sailing initially, but then got becalmed on the last few clues. At the time of solving, I wasn’t 100% certain about a couple of answers (1a, 22a, 21d), but subsequent searching seems to confirm them. Also, I still haven’t fathomed the wordplay element of 9a/20d, so please feel free  to offer enlightenment.

Across
1 BERTH A - The final one I solved (after several minutes). I doubted whether there was a St Bertha, but it turns out that there is. However, given the punning nature of the wordplay “first job?”, perhaps “Woman” would have been a fairer definition than “Saint”?
5 BROOD HEN (on bed or h)* - nounal anagram indicators seem to perturb some people. But sparing usage, such as “contraption” here, seems reasonable to me.
9,20d SLEEPING PARTNER - I’m not sure what the “out east, perhaps” part of the clue is alluding to…
11, 7d STAR OF DAVID - (daft advisor)*
18 PARALYMPIANS (army pal in spa)* -  A bit of a clunky clue, both in terms of anagrind (”rallied”) and surface reading. I’m ashamed to admit that it was only several years ago that I learned that this portmanteau word is derived from Parallel Olympics and not Paralysed Olympics.
22 FLETCHER - double def. I figured the oblique reference to arrow-making, but was blissfully unaware of the playright.
28 SKETCHER - K, H in (secret)*. A seamless segue between wordplay and definition. I assume that “letter in” is the anagrind.
29 DRY+DEN - A familiar construction, but I’ve just found out that the reference to “Mac Flecknoe” makes this an &lit! (I must bone up on C17th literary feuds)

Down
2 O+LIT in HE(rev) - I slogged my way through this one. The ambassadorial part came readily enough, but “upkeep” as a reversed container and an inability to get past OT for “old writings” kept me guessing.
3 CRIME in THEA
8 EASTWARD (trade was)* - simple but effective, and a silky-smooth surface.
16 SET(rev)+TIMON+Y(ears)
17 BALL PARK - ref “ball park figure”= estimate (in cliched business jargon). Liked the misleading reference to a “soccer stadium” rather than a baseball one, which is presumably a dig at Wembley (Version 2.0) too.
21 JE+ROME - Another toughie. I had to seek confirmation that “Hieronymus” alone was the definition.
24 HUTCH - ref Starsky & …

A typical Paul effort with clues ranging from easy to difficult, and a collection of words some will know, and others won’t.

I quite enjoy the mental challenge of a Paul puzzle, but wouldn’t recommend him for beginners or for those who don’t want to contemplate drugs and flatulation when having their morning coffee.
ACROSS

5 W(R)IGGLER - Don’t like this clue very much

9 TERRARIA - (rare rat I)* - glass cases that may contain an ant farm or the likes

10 FINISH - homophone of FINNISH

11 DROP CURTAINS

13,2dn BOW-LOVER

14 ADO-PTION (point)*

17 CAP-(<=ARAB-Y) - the largets living rodent, a native of South America

20 LABOUR-SAVING

23 FLAT-US - a typical Paul word, meaning the air expelled when one flatulates

25 0-PP-ONE-N.T.

26 TRYING - double definition, although the second of these is a bit loose

DOWN

3 CORN DOLLY - a figure made from wheat or other cereals, which were traditionally made at harvest time

4 PAR-DON

5 W(HATCH-A-MAC-ALL)IT - don’t have access to Chambers 2003 here, but it isn’t in the earleier version I have to hand.

7 G(h)AN(J)A - ganja is a drug made from hemp.  Interestingly, Ganja is also the name of Azerbaijan’s second city.  You learn something new every day.

8 EISENHOWER - (where one is)* - Dwight D Eisenhower, 34th President of the USA and a highly-decorated US general.

12 00-JAM-A-FLIP - similar to 5dn, I can’t find it in my version of Chambers, or in any online dictionary, but the wordplay leads to this word.  I could be wrong?

15 THIN-GUMMY - another word meaning the same as 5dn - not sure of the wordplay.  The setter seems to be indicating that if something is ghummy it can’t eat? (or be eaten?)

16 LAC(ROSS)E

19 (<=DIM)GET - is midget politically correct, these days?  I can’t keep up.

An entertaining puzzle with a not-too-difficult-to-spot theme. Across the middle of the grid is the phrase POLES APART, which separates 6 across answers, all of which are poles of some description: NORTH/SOUTH, POSITIVE/NEGATIVE and MARIE CURIE and JOSEPH CONRAD (who are Poles, rather than poles).