I figured you'd be hiring someone for the day-to-day operations of running your rental property, considering your distance. I don't have any multi-family properties myself, so hopefully somebody else will give you more experienced advice.
For one, I would find a property manager with some multi-family property experience. From what I can gather, an 8-plex is different than a portfolio of 8 individual properties. The tenant class is more "apartment" minded and tend to be more transitory. Also, many of the systems could be shared, such as heating and hot water, and you could run into community features like a swimming pool or laundry room. There is also the issue of traveling to one location vice 8, but since your manager will be doing the "heavy lifting", including screening tenants, that's shouldn't be a big concern of yours. Basically it comes down to managent. Find a good one and it won't matter much if it's one multi-family or several single units. The opposite is true as well.
Another thing to consider is selling in the future or your exit plan. With individual properties, you can just sell one or two if you need the cash or something. With a multi-plex, you have to sell the whole enchilada or enter into some partnership by selling off a partial interest. Also, depending where you buy, individual units may appreciate more in value (for one, they'll occupy more land) where the small apartment building's value is based more on it's income at the time.
