What physical maintenance should I perform on a MacBook Pro? I have a 2009 and 2013 MacBook Pro (MBP). My wife has a 2015 MBP. I'd love to maximize their lifespans by taking care of them physically. 

What there any physical maintenance that I can perform on our MBPs to maximize their performance and life, and how often should I perform these tasks? Which of these tasks can I perform at home, and for which should I bring my MBP to a specialist (e.g. for part replacement)?

I'm thinking about removing dust, cycling the battery a certain way, restarting regularly, storing it for a certain length of time, cleaning external ports, replacing parts after a certain amount of time, etc.
As long as you use common sense and generally look the MacBooks, you should be right. There's no need to change parts until you need to (e.g. a hard drive fails, a bad memory module, etc). 

So, the number 1 thing I would recommend is to ensure you have a backup regime in place (e.g. by using Time Machine). So, invest in a number of external hard drives and regularly backup your data on all three MBPs.