I'm assuming that instances you mentioned are kafka servers.
Now, to answer your questions:
#1: New created topics info is stored on zookeeper and some of the key information will be loaded to all brokers metadata cache buffer.
#2: You don't have to configure any kind of proxy servers for kafka cluster. It can manage itself to implement the fail-over and load-balancing.
#3: Just assigning an unused ID and data folder is enough like the way you did for those two brokers.
Also remember, because ZAB requires majority, it is advised to use an odd number of machines as the zookeeper quorum.