I think I'm doing something wrong, but I noticed that sometimes it is better to divide the single query on two separate queries and pass the result of the first one as a parameter to the second query. Doe this make sense? Is there any magic under the hood for external parameters vs query variable passed from one part of the same query to another part?
Yes, it makes sense, although you can chain parts of your queries together using WITH. When you do that, make sure that you watch the cardinality, especially when you have UNWIND clauses.
When you decide to use multiple queries, and depending on their type (as in WRITE / READ ) it may be smart to make sure that, in the case of a WRITE query, they are all part of the same transaction. See https://neo4j.com/docs/cypher-manual/4.0/introduction/transactions/