I am looking into deploying a small single SharePoint 2013 farm that will be used exclusively for external communications with clients. I wanted to know what topology option I have. Please keep in mind that this is small deployment with no HA requirements.I also need to be able to completely separate client data from internal data, this includes authentication mechanisms. One of the main things I am confused on is what actually needs to be placed in the DMZ/perimeter network. I have heard conflicting things on this. I want to make is secure but want to minimize the complexity of the farm if possible. Any tips suggestions or words of wisdom would be very helpful. Thanks
A single server SharePoint farm is just that, one server for all underlying components required to run SharePoint. This includes your database server, the databases, the web server, and SharePoint installation. It is the least complex configuration from a topology standpoint but is generally recommended as a non-production environment.
Note that you will still need an Active Directory (https://support.microsoft.com/en-us/kb/2764086) for SharePoint service accounts. And if you plan to use a DMZ then you'll need to configure it such that the SharePoint farm can communicate with your Active Directory. I'm assuming here that you aren't going to stand up a separate AD just for your farm in the DMZ.
And if you don't want to mix your external users with internal users you will need a solution for storing and managing external users outside of your AD. Again, I'm assuming based on your comments that you don't want to share your current AD.
Lastly, if you don't want to mix client data with "internal" data then you are going to need to ensure you use separate site collections for your external content and that these site collection have a separate backing SQL content database.