If you ride a lot, you should do the lowers service yourself. At the shop, the tech is usually going to pull up the pdf instructions for video and follow the steps, just like you would doing it at home. If you make less than $60/hr spending money, it makes sense to do it yourself.
For damper service and seal replacement, you can find a good shop or diy.
You should have an Excel spreadsheet with all your suspension units listed - their model year, date purchased, and ride time. Yes, ride time updated at least monthly.
Follow the manuf. instructions on service interval at first. If your oil or foam rings still look pretty good, you can fudge on that. If they look terrible, go more frequent.
Riding in the dry with a mud guard protecting the stanchions, my foam rings and oil still look good at 2x the Fox recommended lowers interval. But I service my shock more often than recommended.
Air suspension performance begins to degrade from the moment you throw a leg over the bike. It's not in your head.