Sql-server – run concurrent backups of multiple read only filegroups

In short, no, you can't backup the individual files that you want to restore. According to BOL, the only way to backup files on a database that uses simple recovery model is if they are all backed up up together: http://msdn.microsoft.com/en-us/library/ms179401.aspx .
Have you considered differential backups of the files? Doing this would give you smaller file size for backups (still requires a full at some point), but would also increase the number of steps required to restore the database. Differentials partial backups are described here: http://msdn.microsoft.com/en-us/library/ms190218.aspx.

You cannot restore a single filegroup to an earlier state, because that will leave the database in an inconsistent state.

You can restore a database one filegroup at a time. However, as long as a particular filegroup is not up to date with the PRIMARY filegroup, any access to a table that is stored (even in part) on that filegroup will cause the query to error out. Only after all filegroups are restored to the same level (meaning to the same "log sequence number") can the entire database be accessed.