No, Steam Machine is probably not a good idea any time soon. Whether it will receive adequate support or not is not known yet, and it's just a custom-built PC with some price added on top of it. If you want to try PC gaming of some sort, you're better off getting a more traditional gaming PC, trying if it fits you and if not, install SteamOS on it yourself because, you know, SteamOS is just an OS like Windows and Linux, and if you can always install a new OS if you don't like what you already have. Once SteamOS gets to a more mature state, it'll probably be very easy to install (if it isn't already).
EDIT: And just for the record - SteamOS is what makes Steam Machines what they are instead of just regular PCs so that's literally all there is to it (unless you care about having Steam logos on the box as well and unless you really, really want a Steam controller included).
