1. This is just for custom columns.
2. As I mentioned in my previous reply you need to use PGAdmin for that. PGAdmin is installed with PostgreSQL and it connects directly to your database so if you are not familiar with it take care not to make any other unintended changes to your data while using it. To start it click your Windows Start button then type the following:
pgadmin
and click on it when it appears. Double click on "PostgreSQL x.y" (where x.y is your PostgreSQL version) and if your prompted for a password the default is "dbpass" (without the quotes). Next double click on "Databases -> YOUR_DATABASE_NAME -> Schemas -> Public -> Tables -> cash_custom_cache (and/or tourney custom cache for tournaments) and the number in brackets is the number of custom columns which should look
like this. In some cases that number doesn't correlate directly to the number of cached columns which can depend on the custom content you are using - you can see more about this in
this thread and
this thread.
3. It's separate for both tourney and cash so you can have ~1,600 custom columns in each of them.
4. No but once you've reduced the number of custom columns you should rebuild your custom cache.
5. When the limit for custom columns in a database table has been exceeded it isn't possible for PostgreSQL to rebuild the database cache and I am not aware of any circumstance where that wouldn't be the case.