Wait until you can afford the full PC before buying. By the time you finish buying the thing, parts will be "out of date" in that there will be newer parts that drove the older parts' prices down, or allow you to get better parts for the same price you're willing to pay now.
The only definite change I'd recommend, as Bonsai mentioned, is adding a HDD on top of your SSD. The 120GB is fine for normal operations, and I've never had issues with mine, but I've got almost a full 1TB drive of Steam games as well. I don't keep data or anything else there, that's what my SSD is for. The only things on my 1TB drive are games.
I'd probably also recommend a different case as I've never heard of that company, and that case has no current reviews on Newegg or Amazon. If you like larger cases, I'd recommend something in your price range from NZXT or Corsair. There are other brands to look at too, but these two have consistently reasonably priced, well built cases.
The Biostar motherboard isn't fantastic, but it's not bad. According to the VRM list, it's at least okay for
the chart, though not a lot of experience has been posted.
PSU, eh, try to go for something from Antec, PC Power and Cooling, OCZ (uses PCPaC parts, apparently), Corsair, Seasonic, XFX... If in doubt, look for an 80+ certification, ideally bronze or above. I've got an OCZ 700W unit (highly overkill for what I've got) with a standard 80+ cert and it's working great for me. Just some anecdotal evidence, I suppose.
