Hi Alex,
Kitely's $5/month plan includes 30 hours / month (about an hour / day on average). The $20/month plan includes 120 hours / month (about 4 hours / day on average). If you're spending more than 4 hours / day on average in Kitely than you can get the 35/month plan and have unlimited time.
People cover their own time unless you change the default and decide you want to cover their time in your worlds yourself. Kitely's Free Plan includes 2 hours/month (6 hours on the first month). If people are spending more than that amount of time in Kitely then they can buy KC or upgrade their plans. You really don't have to cover their costs.
Please note that when you upgrade a plan during the month you are charged a pro-rated amount of money and receive a pro-rated amount of Minutes during that month.
If you are fine with doing all the backing up and fixing OpenSim problems then that's great. However there are many people who prefer to not have to waste time doing all those things and are willing to pay a reasonable amount of money to have companies, such as Kitely, make sure that everything continues working as it should.