A Lawyer may hire paralegals, clerks, secretaries, and other assistants. The lawyer may hire as many as s/he pleases, and assign them whatever tasks s/he chooses.
However, some kinds of documents may need to be signed by the lawyer (which ones will depend on the jurisdiction, in the US on the state). During the so-called "robo-signing scandal" it was held that, in some US states at least, a lawyer who signs certain kinds of documents without reviewing them has failed to perform the duties imposed on the lawyer by the law, and the documents may be invalid. Large numbers of mortgage foreclosure cases were dismissed when it became known that the lawyer signing relevant documents had not in fact reviewed them (or in some cases had not even signed them, but had permitted a non-lawyer to sign the lawyer's name).
In addition, some functions in some jurisdictions must be performed by an actual lawyer. For example, paralegals and other non-lawyers cannot validly give legal advice. Only a lawyer can represent a client in court. And so on.
I question whether one lawyer could in most kinds of practice keep up with the work of "hundreds" of non-lawyers, but that would depend on the kind of work done by the firm. In the US, some law firms are essentially collection agencies. There a single lawyer with many many assistants suffices, I understand, and that structure is not uncommon in the US.