Yes, starting with version 0.8.5, mailbfr is compatible with OS X 10.5.x Leopard Server.
Basic instructions are given in the enclosed documentation. All options are listed in the online documentation. To see it, issue "man mailbfr".
This depends mostly on the amount of mailboxes and mails you have. Bear in mind, that mail is usually composed of many many small files. Many small files take longer to copy than one large file. A full (or first) backup takes much longer than successive (incremental) backups. The amount of time necessary for a full backup can vary from minutes to hours.
Unfortunately we haven’t found a safe way around this issue yet. You’ll have to live with it. Important: "mailbfr -f" should only be used if your database is corrupted, not just for the sake of it and not just to recover a single user. If you need to fix a single user, issue "mailbfr -m username".
There are pros and cons for each method. Again this really depends on the amount of mail and mailboxes you have.
Although we cannot decide for you, we favor “rotation”. Rotation will make a full backup per week and just add changes on a daily basis.