The method you use to select for what historian is going to be used is dependent on how you want to view and access. the information. If you want to use a graphical representation, you can use Charts e.g. Easy Charts, Bar Chart.
You can also store information using Transactional groups. I am attaching a link with the different option you have with information so that it can assist in your decision making process.
https://docs.inductiveautomation.com/display/DOC79/Historian#Historian-WhatistheTagHistorian? Found the information in the user manual which can be very helpful.
When it comes to whether or not to use a separate server to have your database. I think that depends, on how you are going to be access it. As well as the reliability of your network. In my personal experience I prefer having it on my local server because I will always have access to it and can modify it locally according to my needs.