Some of the data that I (as an investor) find most useful are the following: median sales price, amount of inventory, absorption rate, cumulative days on market, demographic info, crime stats, etc.
No, I'm not overwhelmed, but I kind of felt so at first. Yes, having the data (and knowing how to use it) does help me to narrow the scope of my search, but that doesn't necessarily imply or infer that I might not have 25 (or more) properties to check out (at least in certain areas). I use the data primarily to filter out the stuff that I'm DEFINITELY not interested in, and to limit the size of the set of properties to check out.
OTOH, I prefer to do most of my searching online, and I acquire properties remotely often site-unseen. I realize that this isn't for everyone, and I don't recommend that others try to buy properties this way without first having obtained some training (as I [and some other investors I know] did).
Take your time; make sure you understand the data (and why it's important). And feel free to ask as many questions as you need, and make sure you get your questions answered--before taking the plunge.