What is the best practice for have freelancers to do the system admin and sites?

Dear Sir,
What is the best practice for have freelancers to do the system admin and multi sites?

Now i give them super admin, but some time some one make the site down, is super could down load all the info from sites or FTP? Is they could down all your plugins from hub?

How to give them one site admin only? some time they can not see the network system and can not do the job.

So what is the best practice for freelancers to the all the multi sites.

Thanks!