I have never used a master/slave setup for my mysql databases so please forgive if I make no sense here.
I am curious, let’s say I want to have a master DB and 3 slave DB’s. Would I need to write my database classes to connect and add/update/delete entries to the master DB or is this automated somehow?
Also for my SELECT queries, would I need to code it to randomly select a random DB server?
What you want to use (and research) is MySQL Replication. This is handled completely independent of your code. You work with the database the same as if there were 1 or 100 servers.