First of all, because there is no set manager, the owner probably does not know what the company is doing so, he will probably give it to you for a small price. After buying the company, you should first inquire about the employees (what can they do, what expirience etc.) After inquiring about the employees you need to promote the most expriienced and best employee as a manager. Because they have expirience, they will know who goes where.
I hope this helps.