Many thanks as always, Jolan, for a challenging set of clues.
Here is my stab at them.
1. Over repaired? It doesn’t start! (5)- ENDED?
Mended – repaired, doesn’t start , gives “ended”- over?
2. Heath and fen birds die quickly with bad hearts (5)- ERICA?
The hearts of the words “fEn biRds dIe quiCkly” and “bAd” give the letters of erica, a heath?
3. War paint for a watchdog? (9) - EYESHADOW?
Eye – “watch” and shadow “dog”. War paint is make up, as is eye shadow.
4. Attend dance outside hospital unit (9) CHAPERONE?
Caper – dance, outside H for hospital and one – unit gives “chaperone” – to attend.
5. Gun dog, in shirt, prepared for going on stage, perhaps (6,7)- RIDING SHOTGUN?
Anagram of “Gun dog, in shirt”. People who "rode shotgun" went on stage coaches.
Thanks again.
AB