My spreadsheet column names are different from Wcart's. Do I have to rename them before importing?

No. The import has a mapping step, so you can keep your own headings.

1. Upload your file. CSV, XLSX and XLS files are accepted.
2. Click Next: map columns →.
3. For each Wcart field, choose the matching column from your file in Map to your column. A sample value from your first row is shown so you can check you picked the right one.
4. Fields you leave on — skip this field — are marked "not mapped — will be skipped".
5. Click the Import button to run it.

For variable products, the mapping has a second section for the variation rows.