I would think you're reno budget is probably a little on the low side especially if your talking hiring out all of the work to contractors. Of course if you are putting in some work yourself, depending on your skill level you could drop that number drastically... though then you aren't accounting for paying yourself anything of course, which is what I tend to do to make the numbers work better in my favor, totally guilty on that one!
You should post your estimated rehab costs broken down into specific areas with estimated numbers to them and that would give everyone, including yourself a better idea as to if where your numbers really should be. In my experience looking at 1970s-80s 4-plexes which are very common in my area, I've been at the 10k mark per unit for renovations easily with properties that aren't in total disrepair so I'd think you should be closer to 15-20k per unit if you're assuming worst case. Post some updates as you find out more about the property.