Hi Adam,
A good point to start would be to take a qkview file of the system and upload it to iHealth (ihealth.f5.com). That will give you most information that you're looking for in one overview. (https://support.f5.com/csp/article/K27404821)
In the GUI, you can also find most of the information you are looking for via the Statistics section (Statistics ›› Performance Reports).
When it comes to hardware refresh, you're best off talking to an F5 presales engineer though as they'll have a good idea of what to exactly look out for as well as proposing new systems to replace them with.
Hope this helps.