Hi,

You should start out by mapping what instances require DTC as it's not something you automatically need (after SQL Server 2005, which did require it for cluster installation). SQL Server uses DTC for things like Linked Server, Distributed Queries and Remote Procedure Calls to name a few. Once you've figured that out, you need an estimate on how much their going to be used and based on that decide number of DTCs.

When you know the number of DTCs you want to run on your cluster there's few things to consider. If all your instances use DTC directly, or features that require it, it might make sense to add DTC to every FCI and have it in a same resource group than the SQL Server. This way your DTC is also always in the same node than the SQL Server, but it adds one more thing to your SQL Server that can cause a failover. If only few instances use DTC and they don't use it a lot, you might go with one or two clustered DTCs in their own groups. This way they might end up to different node than the SQL Server using them and they require their own disk, name and IP each.

If you don't know wether you need DTC or not and how much their used, start with simple setup and have one, then monitor the performance and if you need more then add some.