Hello Chad,
There is not really a best practice. One of the guidelines is to look at the size of the databases, and the number of items in the archives.
Here is my 2 cents:
A new VSG is really only necessary if the fingerprintdatabase is extremely large. I would not worry about this one.
A new VS, also check the belonging database. Remember that creating a new VS also means creating new Journal Archives in this VS, and adjusting the target archives in the Journal Mailbox definitions.
New partitions. YOu can have as many partitions you want. I take in account if the partition can be backed up in a reasonable amount of time. If using a Centera, there is no issue. When using other storage, it might be good to have a partition per quarter/half year/year, it really is up to you. You can even de per month. Good thing is you can prepare your partitions, and define a roll-over schedule.
Indexes can grow pretty large, but should be about 13% of the archived data. In your scenario, 4TB per year = 550GB indexes. I have index-locations which are 900GB... But, same applies here in regards to backup. Can you backup the indexes in a reasonable time-frame. Be advised that as of EV10 you can close an index location, which then menas no new data is added. If you have 64bit indexes (which I assume you do) there is no performance loss what so ever..
I hope this helps. You can also have a look at the Performance Guide on the site. The one for 11 is here: http://www.veritas.com/docs/000004125 that has some indications too.