For apps to open the CSV, I would mention NotePad and the likes.
Would give an exemple row woth an empty field 1,,3
Would mention that the 1st row is usually the field's name
No support for relationships between different "tables" : Not directly, but if files containt IDs, the files could be liked afterwards
Would mention that csv can be compressed a lot and we could be surprised by the files original size. Thus, opening a file could be long, if not possible in some cases.
In the spreadsheet section
would give some more explanations on the configurations that can be changed: separator, charactor set
would explain how to export in csv
Excel 2003 is limited to 65000 sometings rows
What about databases? From MSAccess to MariaDB, Postgres and the likes
Would be nice to provide a small .csv file and the equivalent in other format, so people could compare, try to convert by themself and check if they have the good result.
Useful not only for data.okfn.org but also openspending etc