Hi Luicid!
I’m no expert and I’ve never used this plugin 
This is a great question and I’m afraid I can’t answer precisely but maybe I can give some pointers as you seem to know a bit about coding (since you’re migrating from scratch)
The voting plugin uses 2 tables:
discourse_voting_topic_vote_count
| Field Name | Type | Constraints |
|---|---|---|
| id | serial | primary key |
| topic_id | integer | foreign key (references topics), can be null |
| votes_count | integer | can be null |
| created_at | timestamp | |
| updated_at | timestamp |
discourse_voting_votes
| Field Name | Type | Constraints |
|---|---|---|
| id | serial | primary key |
| topic_id | integer | foreign key (references topics), can be null |
| user_id | integer | foreign key (references users), can be null |
| archive | boolean | can be null, default false |
| created_at | timestamp | |
| updated_at | timestamp |
You may be interested in the plugin’s settings as well but I guess you’re already aware of them 
Finally, topic voting must be enabled per category, so I’d enable them during the category creations in the import script.
As for how to properly populate the votes in the topic during a migration, I’m not an expert, but I guess I’ll go with having random, unique users for each vote, as a job prevents multiple votes from the same user and would delete duplicate votes:
I’ll populate the necessary fields (to be determined) and let jobs fill in other fields if there’s such a thing.
You may also want to have a look at all the plugin jobs discourse-topic-voting/app/jobs at main · discourse/discourse-topic-voting · GitHub
I hope this is helping a bit and that you’ll share how things go