My father was an inner city landlord for a long time before he retired. He never really had difficulty finding tenants, you just have to be very particular, use credit checks, etc. And he never accepted Section 8. It is a pain in the butt to deal with and the quality of tenant is lower. He was also very up on all of the laws and always followed them. You just don't want to mess around with that stuff. He would do much of the maintenance himself (including roofing), but never messed with electrical or plumbing issues, it is just too much work and too many hidden problems can exist.
He lives in the Toledo, Ohio area and could often find properties to buy for less than $20,000, which he could rent for $350-$500 a month depending on the area, and a lot of those didn't require much fix up work (toledo is a lot cheaper than the boston area as nice 5 bedroom homes in the nicer suburbs go for under 200k). Obviously those aren't exactly the good areas of the city, but if you are just starting out the inner city houses are a much safer investment in that if you totally flame out, you aren't out nearly as much money and you can get a lot more cash coming in a lot quicker (since you can buy more house more quickly). You also won't need loans or nearly as much in a loan, so you won't have to tie up other collateral. If you buy houses out in the suburbs or by colleges, you are going to spend a lot of money on the house, which won't leave you much wiggle room should there be a problem, and won't allow you to expand quickly at all.
Also, as long as you do your homework and keep an eye out, I'd rather have an inner city family living in my home than 6 college students. The money will be a lot less with the family, but you will keep the house occupied a lot longer and it will be in better condition, which means you won't have empty houses and won't spend near the time or money in maintenance, allowing you to buy more houses or spend more time on other activities.