Austin,
You are getting some good solid advice above. I currently (just a few months ago) bought my rental property, a duplex. We bought it at steep discount at an estate auction..... about 66% of assessed value, which is pretty accurate in our area as to selling price. We paid 77K, did less than 1K in upgrades, and have it rented bringing in $1350 month. It IS an older buiding, but has newer roof, windows, furnaces, water heaters, etc.....
I am looking at other properties right now too. There is only one triplex that just came for sale in our town. It is a foreclosure and needs some work but is just 26K. Probably needs at least 30K in work (siding, roof, flooring, paint, etc..). I am running numbers at an 'all in' of 72K, and anticipated income of $1400 month when fully rented. At 25% down, this gives a 25% plus return on equity, which is what I mainly look at being a long term investor looking to at returns over 15+ years.
I use this simple, free calculator from here
http://dinkytown.com/java/InvestmentProperty.html
to run my numbers. I agree 100% with the 'guide' of expenses running 50%, at least for analysis purposes. This particular property came in at 45%, partially as it will have new siding, roof, some mechanicals etc....
I also agree with the general feeling of many hear that you are going to have a bit higher turn over in a typical unit like this than a SFH. I figure 1 month a year, and if less, icing on the cake. My 'mentor', who works for me in our 'day jobs' has about a dozen units and just had one turn over where the tenant was there for about 7 years! BUT, on average, it seems he has a tenant stay about 1 1/2 - 2 years.
Good Luck,
Dan Dietz