If my Fidough was damaged, and I evolve it to Dachsbun ex and use the "Time to Chow Down" Ability, does that Dachsbun ex also get healed of all damage?
Yes.
Source: Stellar Crown FAQ; TPCi Rules Team (2024-09-12)
If I use Dachsbun ex's "Time to Chow Down" Ability, can I choose which of my Evolution Pokemon to heal so I don't have to discard Energy from one of them that has just one damage counter on it?
No, you choose to use the Ability or not. Once you choose to use it, you have to heal all of your Evolution Pokemon and discard Energy from all of them that were healed.
Source: Stellar Crown FAQ; TPCi Rules Team (2024-09-12)