Does csv field order matter when indexing?

Elastic Stack Logstash
1

If I have logstash reading csv files, with fields in a particular order, and then I change the order in both the new csv files and the logstash config file, does logstash and/or elasticsearch care?

If I also add new fields into the csv records, does logstash or elasticsearch care?

In both cases, elasticsearch will have records with both the old and new order and fields.

2

I change the order in both the new csv files and the logstash config file, does logstash and/or elasticsearch care?

No.

If I also add new fields into the csv records, does logstash or elasticsearch care?

Assuming you adjust Logstash's csv filter for the new columns, no.