FoundationDB cluster configuration

Which one is the recommended approach in configuring fdb cluster, when i have nodes on 3 datacenters:

a. having storage service, transaction service and stateless service run on every node of the cluster
b. having x number of nodes for storage only, y for transaction only, z for stateless only

How do I decide how many resolvers, proxy , transaction servers are needed when there are different types of clusters having 9 nodes to 75 nodes in each cluster, heavy read and write workloads, around 1TB of key-value data.

I see in the documentation that default commit proxies and log servers is 3, GRV proxies and resolvers is 1. For a cluster with nodes in 3 DC’s, 75 nodes and each node have storage, transaction, stateless process configured. Please suggest.