We have a 2.1TB DB, split across the primary and 3 FG's w/ 8 files in total.

We want to setup DB Mirroring using High-safety mode, since we are only running standard edition.

A few questions
1) How much log disk space should we plan for of a DB of this size?
2) How much of performance hit will we take implementing High-safety (Synchronous) mode instead of High-performance (Asynchronous) mode?
3) Since we're switching to Full recovery in order to use DB Mirroring, I assume this means we need to (start to) take regular backups in order to reclaim the log space otherwise the log files will just continue to consume disk, right? I'm not saying this is a bad thing, I just want to make sure my assumption is correct.

to clarify 3, we would do something like weekly full db backups, and then maybe twice a day (?) log backups, when we backup the log, will the log file size automatically shrink (to 0) or do we need a maintenance task setup after the log is backed up to shrink the file?