You forgot one thing

binlog-do-db=our_database  
binlog-ignore-db=mysql  
binlog-ignore-db=test  
replicate-do-db=our_database  
log-slave-updates

The option log-slave-updates takes SQL that was read from relay logs and records them in the Slave Binary Logs when the SQL is completed.

Please be very careful. You should never use binlog-do-db and binlog-ignore-db simultaneously. I wrote about this back on Jun 14, 2012 ( Configured MySQL replication but its not working ) which points to an old Percona article on binlog-do-db being dangerous.

SUGGESTION

Of the things you are using, you only need these lines

replicate-do-db=our_database  
log-slave-updates

You really don't need binlog-do-db=our_database once you have log-slave-updates working properly.

The simple answer is No.

In Mysql replication, Master copies the bin log files to slaves, and after that, it's work is over. Now the Slave will run the bin files and execute them, but there won't be any performance on Master.

There might be scenario where you are using full synchronous replication, in which master will wait for the slave to execute the query, but again it won't impact the performance in terms of memory or CPU, but the master will wait for the query to be executed.

Also, for your second question, Phil already answered it, that ssh sends data through encryption which uses a lot of CPU, hence if you want other ways, use the other methods which are described by Phil.