I have noticed MP has some bugs when it comes to following, liking, and reposing sometimes. I also receive the error time to time that there is no more accounts to follow blah blah blah. But really there is.
Usually the above error is caused by proxy issues, or the fact that you actually ran out of users to interact with from your source list. A good way to rule out whether or not you are indeed out of users to interact with is to add a few popular hashtags into the follow or like source. If the account is still not interacting with users, then its not because you do not have any other users to interact with. Instead it would be a proxy issue or something else.
Yes I follow and like in the same day between 10am-2am
I personally do my best to keep my sources as full as possible. On average I have between 100-300 sources. I use a mixture of highly popular accounts, and smaller accounts.
Yes, in most cases I will use the same sources for other accounts in the same niche. It just depends on the account and what my specific goals are.