To do a backup of your database : mysqldump -u OCS_USER_NAME -p OCS_DATABASE_NAME > yourbackup.sql
The limit of the database is something like 10^12 computers in database. There is no reason to reach the limit :). The biggest inventory we had in reference was 250000 computer in database.
As windows is a demo plateforme that must never use in production for OCS : use a linux server if you don't want to have problem with performance and security hole (and have latest version of OCS with all cool newest feature).
For change the time interval, look the parameter FREQUENCY in the configuration option : By default, it's set on Once par day (24h) and we don't recommand to use lower value.