Thanks for these great clues, Jolan.
Challenging and witty as always.
Here is my rather rushed stab at them.
1. Jumping every hedge, unicorn tops any fast and furious driver (4)- JEHU? – tops of “Jumping every hedge, unicorn” gives the name of a Biblical fast driver, extended to any of that type?
2. Arrangements to re-use a last site, withdrawing seats not occupied (2,7)- AT LEISURE? – anagram of “reuse a last site” without “seats” gives “at leisure”- not occupied?
3. Anything manufactured in the same place as another established pair (10)- STABLEMATE? Established- stable + mate-pair gives stablemate, one of the Chambers definitions of which is “anything manufactured in the same place as another”?
4. Solitary sour-tempered person lives in cast-off coverings (6,4)- HERMIT CRAB? – Solitary – Hermit + sour tempered person – Crab giving Hermit Crab, a creature that lives in cast off coverings
5. Tsarist rock group? (4,7)- Very very long shot – CAVE ARTISTS? Rock is anagrind giving “Artists” from “Tsarist” and definition is Rock group – cave artists?