Duplicate Detection Rules Limitations

Hi Community,

I have few questions on the duplicate detection rules,

1. I wanted to know if the rules get unpublished if we import a solution to the dynamics 365 CRM environment? 
2. If yes does the rule run on all the existing records(for eg Lead) present in the system run again?
3. What happens to the new records if we try to create new record (Lead)?
4. Is it recomended to use Duplicate detection rules or is it good to have a plugin running in the background?

Looking forward for the kind responses.

Thanks all