If you do a Search for Osobike you find a smattering of comments, mostly poking fun at the guy that started the company.
Osobikes come with coaster brakes which don't stop you that well. If you get that bike, get at least a front caliper brake put on by your bike shop.
Building your own isn't a cost effective way to get rolling unless you've got a pile of unused parts lying around. That's a nice frame in the pic but it's got vertical dropouts which will make it difficult to convert to SS/FG.
BikesDirect sells the popular Kilo TT which has been recommended a zillion times for the newbie on a budget. They sell other SS/FG models, too.
IRO bikes are also quite popular and you can customize your components they install or they'll send you a kit and you put it together yourself. Lots of options. They'll even get the frame painted to whatever you want, for a price.
And the Bianchi Pista is so popular nobody rides them anymore.
First off, decide what type of riding you want to do: tricks and skids, riding fast and looking cool or commuting to work and lugging groceries home. Different style frames for different riding.