Learn English – Does ‘fall in with’ always have a negative connotation

It very much depends on the tone of voice with which this is said. It can simply represent a casual way of voicing agreement, but if you're not careful, quite easily apathy.

Once again, this depends on the context. I could see this sentence sounding just fine, or sounding a bit awkward, depending on the circumstances.

Let's say your company is about to hire a new person, and you will be that person's supervisor. A search committee is in charge of the hiring. You've looked through a stack of résumés, and brought three finalists in for interviews. One person (I'll call him Joe), has impressed everyone greatly. During a meeting to discuss the final details of the hiring, the discussion goes like this:

Committee Member: "Well what did you think of Joe?"
You: "Oh, he impressed the heck out of me. I'd love to have him work for me."

That remark shows you're enthusiastic about making him a member of your team. Assuming you're a fair boss who treats your workers with decency and respect, there's nothing negative about that statement; it conveys respect for Joe's potential.

Then again, we could change the scenario around, and a remark that sounded enthusiastic and positive can suddenly sound domineering and creepy. Assume a team of well-credentialed professionals have been hired to do some kind of work, but you like to take advantage of that, and frequently assign them menial tasks. You ask them to walk down to the company cafeteria and bring you back coffee. You give them menial secretarial work, such as asking them to retype memos for you. Another manager in your company thinks maybe you're abusing your authority, and decides to mention that to you:

Follow Manager: "Don't you think maybe you're asking your engineers to do a few things outside their job description?"
You: "What's wrong with that? I want them to work for me."

In other words, there's nothing inherently wrong with alluding to the fact that the employee works for the employer. I work for my boss, and I wouldn't be insulted if my boss said that I work for him.

If you ever say something like, "I want him to work for me," and you think it may have sounded awkward, then you can always follow that up with something like, "I think he'd do a great job," to emphasize how you meant your remark as an indication of respect for that person's abilities, potential, or work ethic, as opposed to some selfish gain.