1a. In stupid form, a chore to translate?
HORACE
Yes it's an anagram but what's 'in stupid form'?
4a. Water flow barrier impedes a good deal, maybe.
ADAM'S ALE
I get the parse (a-dam-sale). Is Adam's ale water?
17a. Headgear VIP doesn't have on
TOPPER
21a. Windy place, cold for Romans here in the past
CHICAGO
I get the parse apart from the Roman connection
23a. As economist,make distinctive mark on hard currency.
MILL
3d. City appears smart to Lady Stanhope
CHICHESTER
Parses for the above please.