1) When you change the recovery mode to Simple, you would loose your ability to do a point-in-time restore of the database. If you are not familiar with point-in-time restores, search the Web or talk to your SQL Server expert. Before you switch to simple recovery mode, you should consult the database application owner and/or your SQL Server expert, it could be an application requirement not to use simple recovery mode.
2) You would need to run a log backup to truncate the logs. There is no other way in BE. Alternatively, you can use the SQL DBCC to truncate the logs. In this case, you don't have to do a log backup, but you would have to do it manually. With a log backup, you can schedule the log backup job.
Once you truncate the logs, the error message will go away. Whether you backup and/or truncate the logs, the ability to restore your SQL database depends on your database backup. As long as your database backups are good, you can restore your databases to the point of the database backup. You would not be able to do point-in-time restores without your logs.
