Self-management is the way to go in establishing your career as a musician. Much can be learned by taking on the jobs of securing gigs, getting varied licensing deals, getting some publicity, planning tours, dealing with personal issues that arise within the band, and whatever else is needed to stay on course.
These days doing your own management may be what you do for the rest of your career. However there MAY come a time when the daily tasks of doing the business of being an artist take up too much time, and it is then that the services of a good manager can be very useful.
I have always felt that if any musician or band has worked hard to establish their career and achieved a modicum of success, they will have a better chance to 'attract' the services of a professional, well-connected, and respected manager.
Managers who do this job for a living can only take on clients that generate income.
Making money as a personal manager is no easy task, and many upcoming artists forget that if any amounts of money are to be generated from their music, it can take years for the flow of that income to be reliably there. So, as a band develops self-management, or gets help from intern/student manager-wannabees, this can help pave the road for professional management.
Personal managers get paid a negotiated fee (20%-25%) for their services (get it in writing) for any and all business transactions they are responsible for over a particular contract period.
One of the most important jobs of a manager is to secure recording and publishing contracts for their clients, this is why it is so essential to choose well-connected and well-respected managers.
The music business is a 'relationship' business. Who knows who, and who can get to know who, and who did what successfully for who. This is what the management game is all about.
So, don't be in a hurry to 'get' management. You could be better off just keeping your hands-on business the way it is.