I will admit I have no experience in owning an apartment complex, however I have worked for a property management company and I know plenty of people who do own rental properties (particularly multi-family complexes). Like you, I plan to buy a 4-plex in the near future and have spoken to those with experience on the same problems you brought up.
Here's what I've learned:
Obvious, location plays a huge part in whom you rent to. Bad side of town, likely bad tenants. You can higher a property mgmt. business, but keep in mind, they prefer to manage larger quantity and they may not have your best interests if you don't own at least 12 units. However, that's just something to keep in mind, it isn't a rule - there are plenty of PM out there that are willing to manage smaller properties and do a good job at it. But be active with your property and make sure you know just as much of what's going on with the properties as the PM does.
In terms of repair, as a home owner who has done personal repair to his own property, trust me - the internet is your friend, especially YouTube if you're a visual learner like I am. Something that may seem overwhelming at first is simple once you've done it a few times and you start to wonder why you were so worry about it! Changing a sinks, bathtubs, toilets and putting down tiles and fixing a wall is far easier than people think it is. Rule of thumb, if it doesn't cost more than a few grand and weekend to do it, unless time is something you just don't have, you can do it yourself.
One site I frequent and get taught a lot on Real Estate investment is Bigger Pockets. They have an entire system set up - for free - that helps new investors and the forums friendly and more than happy to answer an questions you have on getting started. You might even find so mentors in your city who're willing to meet up and teach you a few things.
Every financially secured individuals I personally know, who doesn't have a fancy college degree, got there through real estate - particularly multi-family investments. I wish you the best of luck and I hope you share your experiences (good and bad) here so those of us who are aspiring Real Estate Moguls can learn from your experience!