I have several questions.
1 - How do they collect monthly fees?
You deposit coin. They give you a credit and you can see how much credit you have at the top of your dashboard. The credit declines gradually until you need to deposit more coin.
2 - How do you tell which card is giving you a problem with this OS? If you not home and you go online to check your rigs and one is having problems. How can you tell with out error codes and such?
The dashboard shows your hashrates and temperatures for your cards. If a miner is offline the background color changes in the dashboard so you can see it is offline. There is also a "simple rig resetter" you can buy to automatically reboot frozen/crashed rigs.
3 - How often is this OS updated?
Frequently. With this OS most updates are pushed out automatically. Some people like the automatic updates. Others dislike it. It's just a personal preference. Major updates like kernel changes or whatever may require you to manually update if you want to test the updates before they're made live.
Other OS do not update automatically.