Dynamics 365 For Finance and Operations has pretty decent documentation available on how to configure and setup an environment. However, some areas need some additional detail to really help them be ready for prime time. Specifically in the area of describing your proposed environment, things are sort of high level. The official documentation can be found here.

ConfigTemplate.xml

I've given this file its own post with lots of detail to hopefully help with some of the fire points that need to be specified here.

DatabaseTopologyDefinition.xml

This is actually pretty straight forward compared to the ConfigTemplate.xml file. There are some values that are duplicated between the two which I call out below plus some additional documentation to help decide what names to use. This is also available for download.

<?xml version="1.0" encoding="UTF-8"?>
<!-- Configuration Template for a Microsoft Dynamics 365 for Operations, On-premises deployment 
        with additions from @NathanClouseAX from atomicax.com. This file is meant to be paired with the configTemplate.xml file found here:
		http://www.atomicax.com/article/d365ffo-prem-configtemplatexml-deep-dive -->
<DatabaseTopologies>
  <DbServer>
    <Security>
      <User refName="gmsaFRAS" type="gMSA" />
      <User refName="gmsaFRPS" type="gMSA" />
      <User refName="gmsaLocalAgent" type="gMSA" />
      <User refName="axserviceuser" type="DomainUser" />
      <User refName="gmsaAXSF" type="gMSA">
        <ServerPermission>ViewServerState</ServerPermission>
      </User>
	  <!-- userName is the actual SQL user used. This value should match the value defined in ConfigTemplate.xml-->
      <User refName="axdbadmin" type="SqlUser" userName="axdbTESTadmin">
        <ServerPermission>ViewServerState</ServerPermission>
      </User>
    </Security>
  </DbServer>
  <DatabaseTopology purpose = "AOS">
	  <!-- dbName is the actual name for the database for the transaction data database. This value should match the value defined in ConfigTemplate.xml -->
    <Database refName = "axDB" restoreEnabled= "true" dbName="AXDBTEST">
      <Security>
        <User refName="gmsaAXSF">
          <UserMappings>db_owner</UserMappings>
        </User>
        <User refName="axserviceuser">
          <UserMappings>db_owner</UserMappings>
        </User>
        <User refName="gmsaLocalAgent">
          <UserMappings>db_owner</UserMappings>
        </User>
        <User refName="gmsaFRPS">
          <UserMappings>db_owner</UserMappings>
        </User>
        <User refName="gmsaFRAS">
          <UserMappings>db_owner</UserMappings>
        </User>
        <User refName="axdbadmin">
          <UserMappings>db_owner</UserMappings>
        </User>
      </Security>
      <DbTuning>
        <SnapshotIsolation value="true" />
        <ReadCommittedSnapshotOn value="true" />
        <RecoveryModel value="Full" />
        <DBFileGrowthMB value="200" />
        <LogFileGrowthMB value="500" />
        <LogFileSizeGB value="5" />
      </DbTuning>
    </Database>
    <Database refName = "tempDb" restoreEnabled= "false" dbName="tempDb">
      <Security>
        <User refName="gmsaAXSF">
          <UserMappings>db_datareader,db_datawriter,db_ddladmin</UserMappings>
        </User>
        <User refName="axdbadmin">
          <UserMappings>db_datareader,db_datawriter,db_ddladmin</UserMappings>
        </User>
      </Security>
    </Database>
  </DatabaseTopology>
  <DatabaseTopology purpose="Orchestrator">
	  <!-- dbName is the actual name for the database for the orchestrator database. This value is not specified in the configTemplate.xml file and is only specified here-->
    <Database refName = "orchestratorData" restoreEnabled = "false" dbName="OrchestratorDataTEST">
      <Security>
        <User refName="gmsaLocalAgent">
          <UserMappings>db_owner</UserMappings>
        </User>
      </Security>
    </Database>
  </DatabaseTopology>
  <DatabaseTopology purpose="MR">
	  <!-- dbName is the actual name for the database for the orchestrator database. This value is not specified in the configTemplate.xml file and is only specified here-->
    <Database refName = "financialReporting" restoreEnabled = "false" dbName="FinancialReportingTEST">
      <Security>
        <User refName="gmsaLocalAgent">
          <UserMappings>db_owner</UserMappings>
        </User>
        <User refName="gmsaFRPS">
          <UserMappings>db_owner</UserMappings>
        </User>
        <User refName="gmsaFRAS">
          <UserMappings>db_owner</UserMappings>
        </User>
      </Security>
    </Database>
  </DatabaseTopology>
</DatabaseTopologies>

NodeTopologyDefinition.xml

This file actually doesn't require any modification. It simply lists some rules for what is required for each node. There are no real configurable values you have to change.