There are many service providers who help develop content strategies full-time and also support them in their implementation. (Including providers like me. But I'm not the only one.) You can recognize a reputable service provider by the fact that he or she asks you questions about the concept and strategy. Of course, it's not always easy to separate the wheat from the chaff until you've found the right consultants. That's always the case. But here too, you can make full use of the experience, common sense and knowledge of human nature that you've probably already acquired in your (professional) life so far.
Counter question: Why should my employees and I publish the articles chinese america data we write for customers under our own names? It is our job to put into words or to revise what others want to express. The baker doesn't eat all his bread himself either.
A good indication that someone can do something and is a good fit for you is their own content strategy: Are you convinced by what they publish in their field of expertise and do you like the way they do it? It's important that the chemistry is right. When someone writes professionally, their writing style is different for each customer and usually doesn't match the style in their own blog.
The question of budget cannot be answered theoretically either. But a reputable service provider will ask you for the right parameters in order to make you an offer that suits your company.
2. The same applies here as in 1: Do thorough research, use common sense. Don't be blinded by technical terms. Facebook communication and advertising are a craft, not a secret science. A reputable service provider will also try to find out with you what they will do for you and where you will be active yourself. This is also linked to the question of output and budget: Here, too, there are no blanket statements, but rather each individual case - but of course typical experiences that can be applied when dealing with a new individual customer. The most important thing is that you set up the whole thing well conceptually and strategically.
Content strategy in your own blog and in social media are closely linked. Smaller companies or sole proprietors make sense to look for a consultant they trust who will initially develop and implement the overall strategy with them.