How to calculate required ressources from a baseline and what should be measured at all?

I have to deal with the following situatiuon: Currently we have - 1 cluster with 5 nodes running 10 instances (SQL Server 2008 Enterprise edition), and - 1 cluster with 2 nodes running 5 instances (SQL Server 2014 Standard edition) in use. All servers are virtual servers running in VMWare. We want to setup a new cluster (SQL Server 2014 Enterprise). In a first step, 1 instance from the 2008 Enterprise cluster and 1 instance from the 2104 Standard cluster are to be migrated. Therefore, my boss asked 2 questions: 1. How many cores do we need (aim: minimize license costs)? 2. How much RAM do we need? My answer was: "It depends ..." Now I have to deliver hard facts by monitoring the next few weeks. Great! (beware of irony) My approach for question number 1: Using perfmon.exe I plan to monitor - **Processor\% Processor Time** (_total and single cores), - **Processor\% User Time** (_total and single cores), - **Processor\% Interrupt Time** (_total and single cores) - is this really necessary? -, and - **System\Processor Queue Length**. The question is, where to get these data from? From the node? From the SQL Server? In the first case it should be easy: the first instance in question - *vsql2008ent-1\instanceX* for the sake of simplicity - is currently running on a node, let's name it node *sql2008NodeA*. No other instances, nor server should run under normal conditions on this node. So it should not matter where I get the data from, should it? In case of a disaster other instances will be running on this node, too. But we want to have a baseline for normal operation. The second instance - *vsql2014stan-1\instanceY* - shares it's node - *sql2014NodeA* - with 2 other instances. In this case I can never be sure, how much cores the instance will truely need for smooth operation, right? So I can monitor the instance. But what does the result mean? It shows the CPU ressources actually used by this instance, only. But would more cores have been used if they were available? So what would be the answer to the question mentioned above? RAM is the other question. Due to several disasters in the past when all instances landed on the same node I have set an upper limit for the maximum server memory for each instance. This limit depends on the available memory of the node (currently 100GB or 120GB respectively). So how to monitor this? If all memory is used up, everything seems clear: insufficient memory. If all goes slow: insufficient memory. But how much memory do I really need? I try to summarize my questions: 1. Where should I get the measures from (node vs. server)? 2. Do I need to monitor the interrupt time, if I want to know the number of cores required? 3. What should I monitor under the given circumstances to answer the question, how much RAM I need (I know: "The more the better.")? Thank you very much for your help! Best regards!