Depends what you want
you could do what you said and should work fine. Not sure how it would work with different time zones if you have them.
I have two instances one in each datacenter just to keep them separate and different time zones. I still use remote collectors just to offload the collection to them from the analytics nodes. More a personal preference than a design best practice.
I then have a federated instance pulling data from my two main "Child" vrops insistence and works ok. One thing to take into account. My understanding of the way the fed management pack works is it reads the metric config file to get a list of the metrics and properties you need and compiles a rest API call for that data. It sends the rest call to the "child" vrops insistence and it is the "Child instance that executes the rest call to get the data and sends it back to the fed vrops. It turns out there is a built in limit to the number of objects a rest call can collect on (think it is around about 4000) before it truncates the file it sends back. because i have 17k VMs i was not getting data back on most of them into my federated instance.
This is a general vrops limit and not a fed MP limit but to get around it vmware wrote a new MP for me that generates multiple smaller calls instead of one big one. Just something to be aware of.
My last bit of advice to save you headaches in the future size you instances correctly and monitor them constantly if you are starting out. Use the SDDC management pack and keep an eye on the vrops sizing dashboard. There are soooo many little things that can creep up on you and you spend weeks trying to troubleshoot for the first thing vmware support will do is check it is sized and if it is not wont support it until it is corrected.
