Learn Russian: Разве он недостаточно компетентен, чтобы управлять компанией? - Is he really not competent enough to manage the company?

This is the negative version of the result clause you are currently learning. Just like достаточно ... чтобы means "enough to [do something]", adding не- gives us недостаточно ... чтобы (not enough to...). The clause after чтобы uses the infinitive управлять because the subject (он) is the one who would be doing the managing.

Why start the sentence with Разве? Could I use Неужели?

Разве is a question particle used when you expect a certain answer or want to express mild doubt—here it translates well to "Is he really not...?". Неужели expresses much stronger shock or disbelief ("Don't tell me he isn't...!"). In a professional discussion, Разве is the natural choice for a probing, somewhat rhetorical question.

Why is the short-form adjective компетентен used here instead of the full form компетентный?

Short-form adjectives are very common in the predicate (when they follow "is/are") to describe states or conditions. They are especially preferred in formal or professional contexts, such as evaluating someone's fitness for a job. Also, short forms pair very naturally with degree adverbs like недостаточно or слишком.

Why does компания change to компанией here?